Does anyone have any good resources on how to do flash loans?

I'm trying to figure out how to do arbitrage but when I try furucombo it always says I'll end up losing money.

Do I need eth already in my wallet in order to do a flashloan? IS there any way to get eth without the high gas fees? I want to do AAVE flashloans?

Does anybody know how… I've been trying to figure this shit out and I feel lost.