Rolling Ability Scores
Strength, Dexterity, Constitution, Inteligence, Wisdom, and Charisma are all Ability Scores. To determine what your character's score will be in each ability, you need 4 6-sided dice, or 4D6.
You will roll 4D6. Reroll any ones or twos you get. Then drop the lowest die roll and total up the remaining three dice.
Repeat this 6 times (once for each ability). Then repeat it a final time to attempt to beat your lowest total.
Record these rolls on a sheet of paper for safe keeping later. You can assign them to your abilities once you choose your race and class.