Point buy is the most balanced way to set ability scores in 5e. Every ability starts at 8, and you have 27 points to spend raising them. Scores from 8 to 13 cost 1 point each step, but 14 and 15 cost 2 points each — so the top scores are deliberately expensive. No score can start below 8 or above 15 before bonuses.
A common spread is 15, 15, 15, 8, 8, 8 (three 15s cost 9 points each = 27) or a rounder 15, 14, 13, 12, 10, 8. After spending your points, you add your bonuses: in the 2014 rules these come from your race, while in the 2024 rules they come from your background (either +2 and +1, or +1/+1/+1). That means a 15 can become a 17 at level 1 — the highest starting score point buy normally allows.
Point buy differs from the two other methods. The standard array (15, 14, 13, 12, 10, 8) is point buy’s "default" spread handed to you with no math. Rolling (usually 4d6 drop lowest) is swingier: it can beat point buy or leave you with a weak character, and it makes each party member’s totals uneven.