sure they do it is mostly built by particles that come after: subject, destiny and object. they are ga, ha (read "wa"), ni, he, kara, made, and many others. there are verbs there are conectives the point is, in japanese there is quite a complex grammar just like english and portuguese

hehe no they speak randomly, and almost hard to understand. lol I'm kidding sure they do have 日本文法(Japanese grammar)

it's kinda impossible to answer what is the grammar. it's the same as to ask "does english have a grammar? and what is it if it has one?"

Yes, it does. Buy a book and it'll teach you.