A radar is like a big ear that listens to echoes bouncing off of objects. But instead of sound, it uses radio waves to hear things that are far away.
Multistatic radar is like having more than one big ear listening at the same time. Imagine a group of friends playing hide-and-seek, with one person looking with their eyes while another listens for footsteps. If there are two people looking and two people listening, they have a much better chance of finding someone hiding.
In the same way, multistatic radar uses multiple radar stations that listen for echoes from the same object. This makes it easier to find the object and get a more accurate measurement of how far away it is. Plus, it's harder for the object to avoid being detected because it can't hide from all the radar stations at once.
Some multistatic radars even use special techniques to make it hard for the object to know it's being watched, like changing the frequency of the radio waves or using multiple angles to listen from.
So basically, multistatic radar is like having lots of big ears listening all at once to find things that are far away and make sure they can't hide.