Muddy is a verb that means to make dirty with mud. You might muddy up your mom's white shag rug if you don't take off your dirty hiking boots before you walk inside.
The meaning of muddy is easy to remember: just look at the root word mud and think about smearing it on something. Muddy is also an adjective that describes something that's dirty and messy. When you're a child, you often end up looking muddy after playing outside, because you've been splashing in puddles and playing in the leaves. Muddy can also describe soil that's waterlogged, like your vegetable garden after a big rainstorm.