Hi,
To some degree this is one of those "how long is piece of string?" questions, because there are always lots of options rather than just one fret position and one finger for each note.
But there are plenty of pointers around. If you want some ideas on finger placement for chords there are some good pictures on this site of a hand shown fretting the chords, along with the 'formula' showing which frets to put your fingers on. Click on the Chord Pictorial link, or here:
Chord Pics
There are also lots of TABs around - including in Kirk's lessons - which show which fret to press on. You can also watch where Kirk puts his fingers in his very useful videos.
Finger selection can vary depending on what is comfortable, what came before, and what is coming afterwards. So whilst the positions in the pictures are the basic starting point, most players will develop different ways of fretting chords depending on the requirements of the music (for instance, you may not need or want to play all the strings) and what fits the chord change sequence best.
When it comes to playing single notes there are also lots of possibilities, as each note can be found in several places around the neck. The general idea is to work with clusters of notes in various positions so that each finger can have a 'patch' to work on, rather than have them all darting about in a confused manner, with your strongest fingers trying to do all the work.
Probably the best way to understand it is to pick an example - a piece you're actually working on - and ask for suggestions on how other players might finger it.
Cheers,
Chris