Do I have to own socks/etf’s before the ex-date to be paid on the following pay date or can i buy on the ex-date?

I'm still learning stocks and I know there's a lot to learn and what might work for one might not work for another. But let's say I find a stock or ETF that the ex-date is today and everything in the parameters looks good to me will you get paid on the pay date or the following one?