Yeah, it seems like it should be impossible but they have actually done it!
There are a few different ways of doing it but the concepts are all pretty much the same. First you have to make the fuel pellet so it’s almost a perfect sphere. One point I probably forgot to mention is that the outside of the pellet is usually solid but the inside is a gas bubble of fuel. Then you point a few hundred laser beams very accurately around the pellet. When the laser beams hit the surface of the pellet, some of the outer layers fly off and force the pellet inwards. The laser beam also helps to push the outer shell inwards.