Generally you would record your scores at one course over 5 rounds (18 Holes each round) Work out the average score over par for the 5 rounds and that becomes your handicap.

For example Round one you had 17 over, then round two you were 14 over and round three 22 over round four 19 over and round five 30 over - your average is 20 and that becomes your handicap.

Hope this helps!!!