I believe you can learn plenty of music theory, notably harmonic (chord) theory, without being able to read standard musical notation. And you can learn/know this stuff semi-intuitively ~ for example, you can understand the relationship among the three or four chords used for so many songs, and be able to easily find the appropriate chords in each of several keys, without necessarily knowing the terms "tonic," "dominant," "subdominent," and "relative minor" [also known as "SuperTonic"].

The super-simple explanation offered by GUEST of 10:55 pm last night is good as far as it goes, but omits a critical bit of information. When transposing from one key to another and counting the number of notes' difference between them, you need to count "half-steps" (aka "semitones"). Each half-step is a single fret on the guitar fingerboard, and some-but-not-all of the "natural" (non-sharp-or-flat) notes are a full step (two half-steps) apart. GUEST's message implies that each natural is the same "distance from the next, and that's not quite true.

Between A and B, there's a note called either A# or Bb; BUT
between B and C there is *no* extra note.
There's a note (C#/Db) between C and D, there's a D#/Eb between D and E, but
there's no note between E and F.
The rest of the scale has sharps/flats between the natural notes (F#/Gb, G#/Ab, and, once again, A#/Bb).

If you can picture a piano keyboard and know how to locate "C," you should be able to visualize and understand this. The black keys are in alternating groups of twos and threes, and the pairs of white keys without a black key between them are B-C and E-F.