If you have $1000 in your account, and your broker gives you 1:100 leverage, then employing all of the leverage you can make 1 lot transactions. However, most likely you will end up losing your money soon. If you trade with 0.1 lot size that means you borrow $10'000 from your broker. In this case your effective leverage is borrowed money divided by own money. That is in this case approximately, but not exactly 10'000/1000 equalling to 1:10
You need to know what you are doing, and practise with a tiny risk.
High,but sparingly used leverage means that you have to deposit less money.