Leverage
This in simple words means how many times is amount of your money multiplied. In other words this is a ratio of required amount of money to the possible size of your trades.
If your broker allows you to open trades on leverage 1:100, it means you can open a $100.000 if you have on your account only $1000.
Example
Imagine you have $10.000 on your account and you trade $50.000 of XAUUSD. This means you opened a position that is 5 times bigger than your account balance, so it is a leveraged position. The ratio would be 1:5 leverage. If you open another position worth $120.000, you will have two trades opened, of combined leverage 1:17.
We suggest that you never open single trade bigger than 1:3 of your whole money, and that the combined leverage is not bigger than 1:20. It means that if you have $10.000 on your account you should not open a position bigger than $30.000 and that all of your open positions should not equal more than $200.000.