This is actually a really tough question, and not an easy one to answer.
The short answer is that we have an equation that explains where all the particles and the forces between them (except gravity!) come from. But the equation didn’t explain why those particles had mass. So, an extra bit of maths was added that fixed this problem, but the outcome was that a new particle had to exist. This was the Higgs boson. It was first predicted 50 years ago, but we’ve only just found it, which is why everyone was so excited.
Another way to think about it is to use the idea of a party! Imagine a room full of people – this is the Higgs field. When someone boring walks into the room, no one else really cares and so this person can walk quickly and freely. They’re like a light particle because they don’t interact with the people at the party.
Now, if someone famous walks in, like Beyonce, EVERYONE wants to talk to her, or get her autograph. And so it’s very difficult for her to get around. She is a heavy particle because she’s interacting with the Higgs field and so has a lot of mass. (But, I’m definitely not saying Beyonce is fat!)
The last thing is a rumour of someone famous at the party. People start talking and grouping together, even though that no one else there, and this is Higgs boson. It’s the field interacting with itself.
I hope that helps to answer your question. Don’t worry if you’re still a little unsure, there are lots of very smart people trying to work out what the Higgs boson actually is!