Hey,
I'm just getting into soldering with the "stick" type (or how to call that) soldering iron. It has basically no temperature display or anything fancy, you just plug it in and it heats up. Provided that this iron is fine, what soldering wire should I use? I am overwhelmed with some people saying that the tin-lead variant is okay, and some that say to use the lead-free variant. I currently just want to solder some switches to wires, so I can plug them into my Arduino. Also, should I solder indoors or outdoors?
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Essentially the only reason not to use 60/40 standard solder is if you are manufacturing to sell.
Just make sure you are in a situation where you are not breathing in the flux fumes, either a fan, open window or such.
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The smoke is toxic. You need to have good ventilation.
Small diameter is much easier to use.
Eutectic is much easier to use.
No acid core.
I prefer lead-free. Lead-tin is much easier to get right.
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Assuming being outdoors solves this issue.
Very impressive setup you got! I would just solder once a month or something, so this would probably be an overkill for my situation.
I think tin-lead is easier to use but if you're afraid of lead poisoning I guess you should avoid it. 
If you choose something else check the melting temperature (it's usually higher).
Get flux-core solder that's designed for electronics. (It's also helpful to have some extra flux in a bottle.)
The flux in plumber's solder may damage the board.
Traditional flux is rosin. It makes an ugly brown mess and it takes "chemicals" to clean it, but it doesn't hurt circuit operation if you don't clean it. It's not used much anymore in electronic manufacturing because of the cleaning-chemicals.
There is "no clean" flux which leaves a clear residue.
Water soluble flux cleans-off with water and it's the most commonly used flux in manufacturing. It has to be cleaned-off or it will damage the board. Most components can be submerged in water (the board should be dried before powering-up) but there are some parts that can't be water-cleaned.
[quote]Also, should I solder indoors or outdoors?[/quote]Outdoors can be tricky because the wind or breeze tends to "blow away" the heat.
...When I was a kid I used to like the smell of it! Probably the rosin flux. Now I'm used to it, and of course I try to avoid breathing it. (When I was a kid I didn't stick my nose in the smoke.)
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Make yourself one of these out of an old PC 12V fan.
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I have an old PC fan laying around, thanks for the idea!
You might be interested scanning thru this thread for some ideas, some 900 entries:
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I’m reading here that lead from soldering fumes is dangerous.
I read there that it’s the flux vapor that is dangerous, as is handling lead. So,def.
Here and there on the internets, so… both must be true, but they are contradictory.
I can’t make unleaded solder work well. I have been using 60/40 or 63/37 solder on a hobby basis for never mind precisely how long, many fewer years of planning to do so left, I’ll probably be OK.
a7
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I have the soldering wire here, it says "Size: 63%" (probably poorly translated). I suppose that its 63/37 then.
Looks similar to this one (diameter on mine is 0.8mm):
Some cheaper solders might not be the best, if you have it try it
Highly recommend buying liquid soldering flux or invest in a flux pen.
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I don't think there has been any serious suggestion that the lead in solder is harmful to the person doing the soldering. The EU has mandated its removal to prevent lead finding its way into electronic waste and landfill.
Also flux fumes being toxic? Come on, get real. Whilst anything in theory could be harmful, millions of bench techs around the world have been breathing rosin fumes for decades. I have. I don't believe it does any actual harm.
HOWEVER, if you prefer to be cautious and avoid unnecessary risk, then moderate ventilation from a fan is all you need.
For my part, I always prefer to use leaded solder 60/40, or 63/37 if you prefer eutectic solder. Lead-free solder needs a significantly hotter iron, and simply doesn't flow or wet as well. Damn nuisance, to be honest.
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Lead-free solder REQUIRES a very active flux to clean the metal an get the solder to wet the metal piece. We use an organic flux that was activated by the heat of the soldering iron. When done clean the joint carefully with water and possibly a tooth brush. If the flux is left, it continues to do it's thing.
Paul
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Asthma was mentioned. Forget whether causing thereof or just making it worse or triggering something.
@Paul_KD7HB noted. I have some flux here, it is inactive since I never use it, but it may be active in the other sense, I'll try it with the unleaded stuff that is also, just now, inactive.
All in all, soldering is probably not the worst thing I've done to my lungs over the years. Maytbe even living where I do instead of where I don't is worse.
On the other hand, I really don't like "tasting" cyanoacrylate fumes in my nose and eyes - I did build a little glove box I use when I am painted the edges of carbon fiber frames with it.
With any luck I will beat any such problems (and global climate change) with my planetary exit. 
a7
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The U.S. and UK governments, various companies, and various schools all disagree with you.
The rest of the paragraph is riddled with fallacies.
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I think flux fumes are about as toxic as wood smoke (which makes sense, given that the most popular fluxes are mostly tree sap.) And less toxic than cigarette smoke. That's in addition to the amounts involved being very small, relatively speaking: most solder is about 2% flux, so if you use up an entire 1lb spool of solder, you're talking about 10g of flux. (more if you use extra flux, of course.)
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I saved a few spools of solder from my previous company. One spool has organic flux. It is Kester SN63PB37 with flux "331" which is an organic flux.
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