The Normal Gacha can be rolled with PP you accumulate. It costs 100 PP per roll, with 1000 PP for a 10-roll. (When space is applicable, you will always do a 10-roll.)
Around 98% of the rolls you make with the Normal Gacha will churn out N-rarity cards. Anything higher than that has considerably reduced rates. While it is possible to roll SS/SS+ cards from the Normal Gacha, they are exceedingly rare, with your chances far below 1%. If you're seriously gunning for an SS card, expect to burn at least 200-500k+ PP.
*The Normal Gacha tends to spit out SS Cards that are 30 Cost or below. This means it can be a decent source for getting older Cards as long as you have the sufficient PP and time to roll.