The fretting hand moves along the neck pushing down the strings against the frets to make the desired notes. To make a note, push down on a string behind any fret. Move the finger as close to the fret as possible without being on top of the fret. This will give the clearest note with the least amount of pressure. Be sure to let each finger take a turn fretting notes on each string. In the beginning you may find that some fingers are easier to control than others. Over time each finger will become more responsive. You can spend time developing each finger individually as you like.
Take a little time to get familiar with the fretboard of your guitar. Just mess with it. After more than 20 years with the guitar I still find that I can always get a little more familiar with the fretboard. Begin working with just one string. Play the note at every fret from low to high and then from high to low. See how it feels to position your hand to reach those notes. Switch the fingers that you are noting with. Some of the notes up by the soundhole will be hard to reach and may never come into use for old time guitar playing. The idea right now is to explore every possible note of each string.
A guitar that is in good repair can faithfully produce a wide range of tones and textures, fretting and playing each note will also let you know if the guitar has any buzzing or issues with the action. While we’re at it, try picking in different places along the length of the string. Pick closer to the bridge and try picking closer to the neck. Notice the variety of tones that are available depending on where you pick. You can use these tonal variations for both dramatic and subtle effects.