They have the so called SOV-structure. This means that they have the Subject (noun/name/pronoun), then the Object (also noun/name/pronoun) and then the Verb. Compare this to the English structure: SVO.
They also use particles between some words.
私はおにぎりを食べます - watashi ha onigiri wo tabemasu - I eat riceballs/a riceball
the particles are:
は - ha, pronounced wa, comes after the subject watashi and before the object onigiri
を - wo, pronounced o, comes after the object and before the verb.
Of course you can change the sentence a lot. You can use adjectives,not use an object, and in Japanese you don't even have to use a subject if it's obvious who/what you're referring to. As the sentence changes the particles sometimes change as well (there are "ga", "ni", "he", "niwa", "no" and probably more that I can't think of at the moment).
This was a very vague explanation! I'm not Japanese myself as you can see, but I've been studing Japanese for a while, and while this makes the grammar sound really weird, it's super easy once you get into it, much easier than any language I've ever studied, like English for example.