Using leverage lets a trader control a larger trade size with less capital than the trade's real value; for example, 10x leverage means opening a $1,000 trade with $100 of capital.
Just as leverage multiplies potential profit, it multiplies potential loss by the same factor, and if the market moves sharply against the trade, it can lead to the complete loss of the initial capital (liquidation); for this reason, using it requires careful risk management.