The Japanese language is considered syntactically a Subject-Object-Verb or SOV language in contrast to English which is considered a subject-Verb-Object or SVO language, as these two example sentences will show.
(1) Ken wa (S) tama wo (O) uchimashita (V).
(2) Ken (S) hit (V) the ball (O).
While it is not possible to move the syntactical elements around in English without a changing its meaning, it is possible in Japanese. Why this is so is due partly to particles (助詞). Particles mark the syntactic role of the word or phrase before it. By doing so this means the entire phrase including the particle can move to any other position within a sentence without losing its marked role.
The ‘wa’ and ‘wo’ in (1) are particles.
The English syntactic elements, however, are not marked whatsoever by particles (particles do not exist in English) and only show their syntactic distinction to other elements within the sentence unit by its relative position to each other. The sentence is therefore the unit. The rearranged syntactic units of (3) below in contrast to (2) has a now a completely different meaning because of the changed positions of the subject (S) and object (O).
(3) The ball (S) hit (V) Ken (O).
So Japanese is considered an SOV language because most often the elements follow this order and not because it is fixed by its position like English. But English learners of Japanese can safely assume this structure for learning purposes.