There are some stages you have to go through in learning how to play the guitar. In effect, you need to become a different person. You stop looking at music and playing guitar from the outside and you start to take action. You can be flexible in the order you take these steps in so don't look at them as progressive stages, just as a basic to-do list. So here are some things you need to know.
You need to know the parts of a guitar and what makes a few bits of wood become a musical instrument. You can go for years without knowing the different qualities of cypress, rosewood, mahogany and the other woods but if you are going to be a guitarist you really need to know that different woods give different sounds and some woods are cheaper than others. When you go looking for a guitar to play you should have some idea about the difference between a Fender Strat and a Squier Strat and the variations within those two models of guitar.
If you are going to be an acoustic guitarist you should do some research into the differences in classical, flamenco and folk guitars and the reason some people play nylon string guitars and some play steel string. If you don't know this stuff, when you go into a music store and look at bunch of guitars hanging on the wall, you literally won't know what you are looking at.
As for knowing about the different parts of the guitar, you can learn the basics in five minutes on the internet. If you are going to be a serious electric guitar player, you will need to learn some technical stuff that has nothing to do with playing the guitar but has to do with how your guitar is going to sound and feel when you play it. It's called setting up your guitar and you can let other people do it for you but you will have more control over your music if you learn how to get the best play-ability and tone for yourself.
Another thing you need to know about if you are learning how to play the guitar is the written language of music. Many guitar players will tell you to take the time and trouble to learn to read sheet music. This involves not only learning what the little dots on the page mean but also the theoretical side of music. Lots of guitar players don't learn how to read sheet music but if you want to be a working guitarist, you will find that there are many advantages to being patient and learning standard music notation.
If you want an easier way to read music, guitar tabs are easy to read and it only takes a few minutes to learn how to do it. If you get yourself a tab editing program like PowerTab or GuitarPro or TuxGuitar, you will be able to hear what the song you are learning is supposed to sound like. Reading tab is about knowing where to put your fingers on the fretboard, but learning to read sheet music is about understanding music from the inside.