Leverage lets you control a position much larger than the cash in your account. At 30:1 leverage, £1,000 of your money can control a £30,000 position.
Leverage multiplies both profits and losses. A small move against a highly leveraged position can wipe out a large share of your account, which is a big reason most retail traders lose money.
Regulators in many regions cap the leverage brokers can offer retail clients precisely because it is so risky. Treat high leverage with caution.