There are 12 notes in the 'musical language' (at least the language us 'westerners' use), these are:
A, A#/Bb, B, C, C#/Db, D, D#/Eb, E, F ,F#/Gb, G, G#/Ab, A
The notes in bold are referred to as natural notes.
Notice:
1) Each 'in between' note such as the note which lies between A and B has two different spellings: A# and Bb, don't be confused by thinking that A# is a different PITCH to Bb, it is not, they both sound exactly the same, it is the key you are playing in which dictates which of the 2 spellings you use, referring to a note as having both # (sharp) and b (flat) is to call it an ENHARMONIC NOTE.
2) There is no # or b between B and C, E and F, this is due to the division of the frequency range which some clever chaps worked out as being best split into 12, ascending 1 note from B to C is exactly the same distance as going between any 2 of the other adjacent notes of the 12 such as A# to B, F# to G, Bb to C and so on.
Each of the 12 notes represents ONE FRET on your guitar's neck on a single string, left to right, right to left, etc. If there are only 12 notes in our musical language then it should make sense to you that once you reach your 12th fret from an open string (such as E for example) you have ascended up the 12 notes available to us and thus landed again on an E note. Each string on the guitar's neck works exactly the same, from ANY POINT, so for example if you play the 3rd fret on (either..) of your E strings (the note is a G) and you ascend 12 frets (to the 15th fret) this note is also a G note. The practice of ascending (or descending) 12 notes is known as moving up/down one OCTAVE (the complete distance between 2 notes of the same name). Once you've got your head around this relatively simple idea you should hopefully begin to see that the guitar neck is not as daunting as it first seemed and you actually have HALF (if your guitar has 24 frets, unlikely if its an acoustic but you get the idea) as many notes to 'learn' as you may have initially thought.
Edit:
If you wish to understand how notes are arranged on the guitar's neck in further detail it'd be a good idea to learn how to play OCTAVES on various pairs of strings on the neck, due to normal fretting hand range and distance (interval) between each string these shapes often skip one string (E and D, A and G, D and B, G and E). If you get these shapes down you'll be able to sidestep if you like from a certain note you already know the name of on the neck to the same note on a different string one octave higher/lower, once again making the guitar's neck a much less daunting thing to navigate.