Hello! It is quite similar to EB. The rule-as-written is: roll your ability scores, 3d6 each for STR, DEX, and WIL, swap any two. Then, your pattern, type, and background are rolled, in that order. However, at your table, you could certainly use a standard array, point-buy, or another method you prefer for the three stats, so long as the total isn't too far from 32 and nothing is higher than 18. You could also simply select your pattern, type, and background if your players know exactly what they want to play as. If I were making pre-gens, I'd probably use standard stat arrays of 14,10,8; 16,8,6; and 12,12,10.
I hope that helps!