To cut through all the mystery and jargon, you do not have a handicap, per say.
In a valid handicap system, what you are provided with is a handicap index. Your index is a decimal number, like 11.8. This is the basis and foundation for a handicap that you receive in any competition you may enter.
Remember, your index is not your handicap.
A handicap index is the measure of a player’s demonstrated ability calculated against the Slope Rating of a golf course of standard playing difficulty (that is, a course with a Slope Rating of 113) (see Rule 5.2 Calculation of a Handicap Index).
A provided handicap is computed by entering your index (decimal number) into a course handicap table (which is based on course rating, slope rating, and par of the course and tee you are going to play.)
Since most courses and tees are rated and sloped differently, your handicap will be different from most tees and on different courses.
For example, if you play the Championship Tees on Course A in Paramus NJ, your handicap (with an 11.8 index), might be 15. If you choose to play the regular White Tees on the same course, your provided handicap might be a 12. If you decide to play the Gold Tees, your handicap might be a 9.
Remember, it is all based on your individual handicap index. And ultimately the handicap tables from different tees are figured using different course ratings, slope ratings, and par.
A valid handicap system uses an average of the lowest 8 of your most recent 20 Score Differentials. It does not matter what year they are posted in, it is the last 8 of the most recent 20 scores.
If you carry an 11.8 index and have a bad day and shoot a 95, do not expect your handicap to go up 5 strokes at the next revision. The 95 you just shot will count only if and when it figures in the lowest 8 of the most recent 20 scores.
This is why it is very important to post all your scores, not just the high scores. So you can get a true and valid measure of your golfing ability.
In a nutshell, this is pretty much all you need to know. It is not all that complicated if you understand the concept and the “Big Picture.”
If you want some advice or even if you do not, get yourself into the GHIN system and get a valid USGA/World Handicap System handicap.
It will give you a real measure of your playing ability, and give you a fair chance in any competitions you choose to enter.