A Higgs boson is one of the fundamental particles in our universe.

All the fundamental particles together form the so called "Standard Model". Most particles in the Standard Model belong to two categories: fermions, and gauge bosons. But the Higgs boson is a unique particle. Its role is to give "weight" to all the other particles. Without Higgs boson, everything in the universe would be weightless.

There is an answer here.

This is difficult to answer because it relies on the theory of quantum mechanics, which requires math and physics that are well in excess of what a seventh-grader can be expected to know. You might want to ask this again in a few years!

All forces have fields that represent the strength of the force. For example, electricity and magnetism are represented by an electromagnetic field, gravity is represented by a gravitational field, and so on. Most (maybe all) of these fields are themselves carried by a particle, called a boson, that delivers the field from the source to the recipient of the force.

One field that is important is the Higgs field, which causes inertia: it is the reason why bigger, more massive objects require more force in order to push than smaller, lighter objects. Like most of the rest of these fields, the Higgs field is carried by a boson, in this case, the Higgs boson.