Morphosyntactic alignment is like when you are playing a game of catch with a ball. When you throw the ball, the person catching it has to move their hands in the same way so that they can catch it. This is called aligning your movements.
Similarly, when we communicate with each other using words, we have to align the words we use with the way we're talking about things. For example, when we talk about a dog, we use the word "it" to refer to the dog. This is called "alignment". We are aligning the word we use with the thing we're talking about.
Now, when we use language, we also have to align the way we use words with the way they work in a sentence. This is called "morphosyntactic alignment". It means that we have to use words in the right order, and use the right forms of words (like adding -s to verbs when we're talking about more than one thing doing the action), so that the sentence makes sense.
So, just like we have to move our hands in the right way to catch a ball, we have to use words in the right way to communicate with each other. That's what morphosyntactic alignment is all about!