Key question

The easiest way to explain it is, say you're playing the following:


You're starting in the key of G (E-string, 3rd fret) and changing keys from one bar to the next (as noted above each bar.) But you can also change keys mid-bar:


Mind you this is the bare bones explanation, but it should be enough to get you started.

I'm crap at doing tabs but above is the bassline for Dance the Night Away albeit in two sections

1- the key the song is being played in is basically the root note. I.e the song is being played in G. It helps to learn your fretboard. What notes are where.

2- the singers voice may work better for that song in G#, so I order for it to sound decent, everyone will adjust to G#.

That's my inexperienced two cents

What a key is, as Marko explains, is a bunch of notes that work together. To learn them, play scales (which are the notes in a key). No one likes playing scales much (it does get a bit tedious), but it is one of those basic skills that you need to build on top of to get better as a player. And it teaches your fingers where to go, so you don't have to think about that as much when you play. Guitarists are playing chords, which are certain notes from the scale, which is where you fit together musically.

Lon's first example, playing G, A, B and C for a measure each is not necessarily changing keys - all of those notes are in G Major. Without more context to define it, I'd say you're playing the G Major scale. So if a guitarist is playing G Major chords, Lon's first example will go great with it, because you're both in the same key. Next time you're with a guitarist, ask them to play a constant G Major chord for you, and play Lon's first example along with it. You'll hear how it fits together. Or better yet (because it will sound better with the chord), here's a new pattern to play. It's VERY easy - you're playing the root, 3rd, 5th, and 3rd in G Major. And keep it simple by playing quarter notes - one note per beat:

Example 1 (G Major)
G|——–|
D|——–|
A|–2-5-2-|
E|3——-|

Changing keys is easy if you are playing a pattern, as you just have to change the root (first note you play) and play the same pattern from there. So to go from G to A in my example above, it becomes this:

Example 2 (A Major)
G|——–|
D|——–|
A|–4-7-4-|
E|5——-|

If you still have that guitarist handy, give it a shot. Have them play G Major for a few measures and play along like you did above, then have them switch to A Major, and make the shift. Play that for a few measures, then have them switch back again. Then do a different change - go from G Major to C Major (moving from the E string to the A string, same pattern):

Example 3 (C Major)
G|——–|
D|–2-5-2-|
A|3——-|
E|——–|

You're now playing a simple song. And if you're like everyone else here, you're hooked.

One more step (you can do this, and you'll love where you end up) - change to D Major:

Example 4 (D Major)
G|——–|
D|–4-7-4-|
A|5——-|
E|——–|

Practice each of those examples with the guitarist, then start playing them in this pattern, each Example for 1 measure, at whatever pace you're comfortable with, sticking with quarter notes. The guitarist should like this, too:

Example 1, Example 1, Example 1, Example 1
Example 3, Example 3, Example 1 ,Example 1
Example 3, Example 4, Example 1, Example 1

That is 12 Bar Blues in G. That's a basic song that you can now jam with just about anyone, playing just about any instrument out there. If you're still playing with that guitarist, they have a smile on their face, but it's probably not as big as the one you have going.

OK, so you aren't really changing keys here, just which scale (chord) you're playing in the key. Each of the scales is in the key of G Major. So let's do it - time for a real key change. Go ahead and switch keys to A Major (just shift each pattern 2 frets up).

ZZ Top's “Tush” is 12 Bar Blues, so is AC/DC's “The Jack”, Chubby Checker's “The Twist”, Little Richard's “Tutti Fruitti”, Chuck Berry's “Johnny B Goode”, Jimi Hendrix used it for “Red House” - the list goes on and on. Learn it, learn to change keys with it, and you can immediately play thousands of songs (See, I got back to talking about changing keys).