Were you using separate flux? If not, I’d highly suggest you pick some up - it’s your best friend. If the solder that came with the unit was still a typical rosin-core fluxed solder, that’s good, but sometimes it’s old and the flux is less effective…plus running the iron that hot can pretty much vaporize the rosin before it has a chance to do its magic. But congrats on getting it done, and your first build! It gets addictive… 
So, I went through a tinning tutorial and followed the steps. Here is what my tips look like now.
Is it typical that only a small amount of the tip gets tinned, or is this the sign of bad quality?
Additionally, I tried melting already melted solder that pooled up on my work surface and the solder just wouldn’t remelt … again, bad quality or user error? Haha
I bought separate flux, but realized after that it said I can’t use it for electrical. I have to buy a different kind.
Also, I’m not really sure what temps are good for what tasks. I’ll have to try to find a reference chart of some kind.
Yes, that’s typical and those tips look good. Actually for storage between uses I like to just mound a fat blob of solder on the tips for protection (oxidation) but as long as you try to take care of the tips in use and keep them coated with fresh solder they should last a long time. Try not to let them sit unused on the stand for too long while hot because that can actually oxidize them surprisingly quickly (can usually be fixed with basic cleaning/tinning). Also, don’t ever use wire brushes or anything abrasive on them if they get black looking or whatever…if you have to as an emergency fix, then ok, but at that point it’s time to switch to a new tip. These tips are multi-layered…usually an iron core with copper over that and then nickel on the outside (or something like that), so if you start to abrade away gunk you’ll often scratch that outer coating and then there’s no going back really. They do make an acrid ammonia-smelling “tinning compound” that can be used for a thorough cleaning and that will usually restore a tip in decent shape to an almost like-new tinned surface…but it’s expensive and if you treat them right you won’t really need that stuff.
For flux, you want non-acidic and safe for electronics obviously. You can get liquid or paste, either is fine although sometimes paste makes things easier. There are “no clean” versions which leave no or very little residue behind, but for flashlights you don’t really need to worry about that - any spatter or spreading can be cleaned up pretty easily with 91% isopropyl alcohol that you can get at walmart or walgreens, etc. The regular fluxes (usually labeled “rosin”) come in different versions, too. There are different levels of “activation”, meaning how aggressively they clean the surface while heated and as the solder is melting. Usually a normal “mildly activated” aka “RMA” is fine for leaded solder and brass parts and gentle enough that you don’t necessarily have to clean it up afterwards (never a bad idea, though). Fully activated (sometimes just “activated”) is good for parts with oxidation that can’t be cleaned well but it’s a bit much for most flashlight and electronics. The paste fluxes are more expensive and have a shorter shelf life but almost any of them are decent except maybe the cheapest stuff from China (which can still be usable, depending). The Amtech and Kester versions feel like $$ robbery but they are excellent. I’ve been working through a small bottle of Kester 186 for awhile…well past its expiration date but it still works great.
When you need more solder, do get decent stuff. I like the Kester 44 rosin core, 63/37 (tin/lead). It’s the happy standard for home electronics and works for flowing emitters, wires, driver-to-pill, springs, etc. It has one of the lower melting points at around 183°C, which is good for us. They have small handy-pak tubes of it for I think $8-$10 depending on size and type…those will last quite awhile. If you want to get into lead-free solder then that changes things (higher temperatures, different techniques, different fluxes). Be cautious with the cheap-cheap solders and much from China - many tales about junk solder and bizarre qualities. The Mechanic brand is decent but often not much cheaper than the pro domestic brands.
CML Supply is a great place to get good solder and flux. Often the “good” stuff isn’t available in small consumer amounts but this outfit repackages products from bulk/industrial products, which is awesome, and it’s pretty much always fresh, too. I just buy direct because they are fast and it’s usually a bit cheaper than their same items on amazon (they may still do Ebay as well). Electronics Solder, Flux and Chemicals - Genuine Kester Products
MTN Electronics also has some solder/flux usually, so if you ever want to order parts or drivers it’s easy to tack those on. Big electronics suppliers like Digi-Key and Mouser also have anything you could ask for but usually their pricing and/or shipping prices are deal killers for small orders.
As for temps, most of the soldering world talks in Celsius instead of Farenheit. With the 63/37 generally you can set your iron around 200-210C and that works…if you need to remelt old solder you’ll probably want to bump the iron up quite a bit. If you’re trying to remelt tin solder then you’ll want even more heat. Play around a little with some junk boards/components and see what different temperatures are needed.
Now…in addition to flux, the solder itself is your friend. Even with clean parts and tips and fresh solder/flux, sometimes it’s a pain to get heat transferred to where you want it, and the solder won’t want to stick. Adding a small amount of solder to the tip before you apply it to the flux for heating the part will help transfer heat so much better. But remember to heat the parts and then apply the solder…when it melts and flows then the parts were hot enough. Don’t rub and poke the tip/parts trying to get the solder to do what you want it to….if you feel the need then there needs to be more heat to the parts, or perhaps the tip is oxidized and not transferring heat very well from the element to the outside of the tip (or sometimes you need to bump up the temp control but don’t let that be your first move if you know you’re in the range you should be).
The melting point of fresh solder is usually pretty close to what’s listed, but the temp shown on your soldering unit may not be what the temperature at the tip actually is. Several reasons for that but this is why the iron is usually set a little higher than the melting point.
Once it clicks, you’ll see how easy it is. Flux makes life great and soldering can go very quickly & be enjoyable.
This was a super thoughtful post. Thank you so much!!
As my first build is complete, I think I’ll make this the end of this thread. I will be studying the information you’ve shared and practicing before my next project.
Thanks to all of those who have shared their knowledge with me. No one made me feel unwelcome, and you were all extremely nice.
Great welcome into the community.
Take care!!