Sooner or later you are going to come to the end of a country guitar lesson and realize that, at the very least, you need to know where the notes are on your fretboard. Sure, you can strum chords for a while and have a good time, but if you really want to play country then you need to move on to boom-chuck and finger picking styles. Either means you need to know what you are playing.
Fortunately, it's not that difficult. There are various aids both free and for sale online, but you don't really need any of them. If you have started with some good basic training you will already be playing chords in what guitarists call the 'first position'. That is to say the first five frets just below the headstock, at the very bottom of the neck (yeah, I know, should be called the 'top' shouldn't it? But it's not), and you should already have realized something significant - the notes on the first E string are exactly the same as the notes on the sixth 'E' string, only pitched an octave higher. Which means you only have to learn the notes on five strings instead of six.
In addition, the fretboard on the guitar is as mathematically exact as the keys on a piano, so each string repeats itself for the length of the fretboard and would continue to do so on into infinity if such a thing were possible. In plain language this means that the 'A' string, for example, starts at 'A' as you would expect and then continues fret by fret in half step increments until it reaches another 'A', when it starts the sequence all over again. And it starts that second sequence right where your guitar manufacturer kindly placed a couple of inlaid dots, unless you are learning on a classical guitar. In that case you should find you are at the fret just before the shoulder, at the top of the neck.
Check this out for yourself; your frets on the 'A' string are (starting at the bottom) A# B C C# D D# E F F# G G# A, with the second 'A' being the 12th fret.
The sequence is the same for every string, only the starting point is different. Just take note that 'B' and 'E' do not get sharped - they are natural half steps to the next note in the sequence, being 'C' and 'F' respectively.
In addition to this, the notes across the keyboard also follow a set pattern and always start and finish on the same note. So, the sequence on the first fret is all you need to know to work out what the sequence on all the other frets is. Starting at the sixth (thickest) string, it goes like this (assuming EADGBE tuning): F A# D# G# C F; and the second fret moves everything up a half step and looks like this: F# B E A C# F#. Once again the pattern repeats all the way up the fretboard. Learn the pattern and the notes will fall into place.
Now, to help with this you can form a mnemonic with the notes, since they never vary, except in one instance; the more stupid this is the better. For example, you could try Arnie's Dodgy Gold Creates Fever. The remember to add BE at the end of a full sequence, so what you get is as follows. Arnie's Dodgy Gold Creates Fever A#rnie's D#odgy G#old C#reates F#ever Before Election and so on, over and over again - or very nearly.
The snag is the 'B' string. Because 'B' is a naturally occurring half-note itself it throws the whole arrangement out by, well, one half-note.
Take a look at the notes on the first fret again, which are, of course: F A# D# G# C F. Using our mnemonic, the fifth note should be C#, but because the 'B' string throws everyone out of step by a half-note it becomes 'C' instead - half a note lower, and then everything else follows suit. So you just have to remember this one little quirk.
Confused? Work at it. I promise you it will all fall into place in the end and once you've grasped the basic rules you'll have them for life.