If you have problems, you should probably add flux (make sure to extract fumes if soldering with flux for a while). Some say there is never enough flux.
They don’t want you to know, but you can extract all the fumes and flavors using only your nose!
Seriously though, flux fumes do have a somewhat nice smell to them.
Depends on brand. And my head always hurts after inhaling them for more than a minute without a fume extractor. (I just use a PC fan and some old who-knows-what HEPA-like filter discarded from ventilation equipment. For quick jobs, I hold my breath and/or move out of the way.)
What it looks like: You shat all over the board.
What it smells like: Nasty chemicals but only when hot.
What it does: it helps distribute heat, and causes the solder to be less viscuous and stick to metals readily.
What it feels like to start using it: Wow, it’s like I just gained one year of soldering experience!
What it feels like to remove it from the board after soldering: Aargh… I swear, one more board and I go buy an ultrasonic cleaner. (Some brands are easier but I usually need to employ a spudger, brush, then alcohol annd Q-tip)
Note that some solder comes with a core that contains flux or some similar substance of that effect.
Cleans and keeps the solder points clean. Prevents oxygen from reaching the solder joint
- It removes the oxide layer from existing surfaces so the solder sticks and flows better
- It increases surface tension of the liquid solder so you get a nice round shape and no whiskers and less bridges
- It helps distribute the heat a bit. It works a little bit like thermal paste, especially when the contact area between the tip and the pad/component is very small.
Generally, flux is your friend and soldering without flux is terrible.
Remember that all the flux you use will need to be cleaned off eventually. That can sometimes be a pain if there’s a lot.
