Usual method is that the "1" is the key chord, and you count up the scale.

If you want to play in key of C, 1 is C chord, 4 is F, 5 is G, etc.

In key of G, 1 is the G chord, 4 is a C, and 5 is a D.

Using the numbers avoids "tying" your notation to a specific key, and makes transposing easier.

I'm sure you'll get more specific comment soon.

John