The difference is:
A) A smaller guitar is easier for children and people with tiny hands to play.
B) A larger guitar body can add volume, depth and resonance to a players sound without adding electronics into the mix.
C) A longer neck adds more frets to the guitar which gives more notes and greater range of play in the instrument.
Personally, if you are wanting to learn to play, I suggest buying a full size. (at least a 37”) When you have played for a while, you will want to upgrade anyways and if you buy something too small, you’ll have to make adjustments to your stye since the guitar will be bigger.
Here is a pretty good deal for an decent into guitar. Also, I would suggest checking out what Fender’s (cheaper) sister company, Squire can do for you. They are pretty cheap and decent for an entry level instrument. Good luck!