Johan,
Certain areas of Colorado are set aside for limited entry. Very few tags are given out each year in those units.You accunulate one point a year for the years you apply. There is drawing for the tags with the people with the most points given preference over those with fewer. If ten people had say 15 points and 20 people had 14 points and 17 tags were alloted all 15 people with 15 points would draw a tag and 2 of the people with 14 would draw. Over The Counter[ OTC} tags are simply that. You can buy a tag to hunt certain units where no points are needed. Typically you will have plenty of company in those units.
That said, I messed up my application last year and did not get a point so fell behind. I still have only have 15PP for elk.