All trading involves risk. Losses can exceed deposits.
Margin call is the term for when the equity on your account – the total capital you have deposited plus or minus any profits or losses – drops below your margin requirement. You can find both figures listed at the top of the IG platform.
At this point, your positions become at risk of being automatically closed in order to reduce the margin requirement on your account.
You can rectify the situation yourself in one of two ways: deposit enough funds to increase your equity above the margin requirement, or close positions to reduce it.