It's really a simple process. You're trying to find the position of the source to the mic (or the mic to the source, depending on how you want to look at it) that sounds best. A good way to go, if you're working by yourself, is to arm your DAW track so you're hearing the output of the mic through your headphones, and then move gradually back and forth and side to side while singing or playing your instrument (whatever you're going to be recording), until you find the best sounding position.
There isn't one "sweet spot" that can be scientifically found, it's more of a subjective observation. What position sounds best to you for the sound you're going after. Don't sweat it too much, just take your time to try out different positioning before actually recording the track. What you don't want to do is just get in front of the mic and hit record. Think of it like a guitar player adjusting the controls on an amp before playing to get the desired sound. Good luck with your recordings!
