Film &foil Capacitors soldering

Stick the pins through the holes, cut off excess wire if needed and solder the pins. Make sure not to solder longer than necessary, especially with polystyrene dielectric.

This answer is so trivial I doubt if it is the kind of answer you wanted, but I don't know a better one.
 
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how to solder thru hole
You don't solder the film or foil, so keep your search simple.

I'm not in favor of YouTube for EVERY question, but soldering does need a movie.

I'd just say that guy uses too much solder. A joint should not look "like a Kiss"; or perhaps a Hersey Kiss starved until its bones (the wire and terminal) show. The way he lays it on you can't tell if the solder "wet" the lead. But good photography!
 
The main thing is to have enough heat in your iron to enable a short duration solder operation. Practice before ruining anything that you’d rather not lose first.

I always figured a count off like “one one thousand two one thousand” and that’s it, back off. Even less for fine leads on polystyrene caps.

Clean soldering iron tip, good technique will be required also.