Lot size, margin & leverage

Hi traders! I have bit of a problem understanding lot size, margin and leverage and the connection of these. So when i try to place a trade on my demo acc, usually i use a lot size calculator, but the numbers doesn't always match my expectations. Also some brokers give different names for lot size like position size, which could also be confusing. I also don't know much about marging and leverage? Is there leverage on every single trade? Can i trade without leverage? For example if i want to trade without leverage and i put 100 dollars on the line and get a 1:2 RR, does that mean i earn 200 dollars? I don't quite get it. Could you please provide usefull infos or videos or links so i cant get a better understanding? Thanks a lot.