I've been playing around with soldering for almost 5+ years and opening up electronic honestly my entire life. I have taught myself everything I know using professor YouTube and Google.
Disclaimer: I am a hobbyist not a pro, these things work for me.
No. 1 rule to soldering is you are heating the component first, not melting the solder.
I can't find the official source for this, I found it on Reddit.
Soldering Level 1:
I started with a $10 plug in the wall soldering iron. I highly advice against them. Heat is spotty and I ripped up more pads then I should have dragging it around. At this level my advice is whatever is in your price range and has temp controls.
There is a big list of kinds of solder. Lead, lead free, rosin core and the thickness. Lead free requires more heat but doesn't have nasty lead. What do I use? Lead. Make sure to wash your hands after using it and not to breathe it in. A small fan and an open space helps this. Rosin is a chemical that helps with heat distribution and solder *sticking better*. It's always better to have. As for thickness, 0.6mm/0.8mm is a sweet spot most agree on.
Solder buy here
Soldering Level 2:
Start thinking about changing out the tips of your iron when it comes to different tasks. I use two tips on rotation. One is a cone tip.
The cone tip is what usually comes stock on any iron. Unfortunately, tip A is usually what you get. As a newbie, heating components while soldering feels scary but an even heat makes it so much easier. Tip A, unless you have a $1000 iron, will never provide a nice even heat and will make it feel like you are soldering with glue. Tip B is okay, but tip C is what I use and recommend. It will help you heat the pad, component and solder together.
Soldering Level 3:
Desoldering. I dropped this down to level 3 because it is something I struggled with the most early on. There are two main tools to help. A pump and copper braid/wick/solder wick. Depending on component type, these work to different degrees of success. The very first thing I ever do before I even touch one of these is reflow the solder on the part I want to remove by heating it with the iron and adding a bit of new solder.
The pump is used almost the same as soldering itself. Use the iron to heat the component and solder and with the other hand, press the pump.
Solder sucker buy here
Copper braid/wick/solder wick is used by placing it on top of the solder joint and heating the braid. Be careful, braid can easily rip up the board if you drag it along the board. It can also take components with it. I recommend practising on some old dead electronics first, its what I did!
Copper braid buy here
Soldering Level 4:
Flux. Flux is either a goo like substance or liquid that aids in soldering. For most basic tasks such as soldering a wire it is not needed. I myself, use it mostly when I am desoldering or soldering very small items. It is used by placing a small amount on the area you plan to solder and soldering as you usually would. Flux has very toxic fumes so I am going to say USE A FAN to help suck away the fumes. A flux pen is perfect for most jobs.
Flux pen buy here
Cleaning. After using flux especially, you need to clean the area where you used it. Unclean flux can cause issue in the long run. IPA/Isopropyl alcohol should be used for this with either a q tip or a cloth. I use microfiber cloth as it doesn't leave any residue.
Spare yourself killing a working device (this is a note to me as well). Buy a solder practice kit on Retro Game Repair Shop. Solder it, then desolder it. It's only $3!