To express period and frequency—in other words, to say how many times something happened per day, week, and year, and so on—we need the a counter with the target particle. See here for an introduction to counters in Japanese.

【Period】に【Number】【Counter】

This structure is most often used with the counter 回, which means “times” (e.g. I go back to my hometown 3 times per year”).

しゅう5回ごかい
Five times per week.
ねん2回にかい実家じっかかえる。
To return to your hometown twice per year.
しゅうほん3冊さんさつみます。
To read 3 books per week.

Note the position of the object particle—before the counter.

In fact, the target particle is often omitted.

しゅう4回よんかいジムにかよう。
To go to the gym four times per week.
ねん2回にかい海外かいがいきます。
To go abroad twice per year.