I had an X account with a box of checks and an ATM card that became my PayPal account at some point. I didn't use it much, but I use PayPal all the time. .that's how he multiplied his money. but I wouldn't call it his start.
first tranche of money came from family. recall apartheid emerald mine half share owned by his step-daughter-marrying inbred father
then he dropped out of undergrad and illegally started an online yellow pages website on a student visa. then his parents' rich friends invested in that and it got bought by HP, iirc, in the pre-dot com bust heydey of free money
then he turned that around to invest in X-as-in-the-PayPal-precursor. and then when that went public then he invested in Tesla and then co-founded SpaceX.
total amount of shit actually invented/created by him: that one website. and then a hell of a lot of lucky timing and free money climate from that point.