YOU SAID:

I'm playing with my friend

INTO JAPANESE

私は友達と遊んでいます

BACK INTO ENGLISH

I'm playing with my friends

INTO JAPANESE

私は私の友人で遊んでください。

BACK INTO ENGLISH

I was playing with my friends.

INTO JAPANESE

私は友達と遊んでいました。

BACK INTO ENGLISH

I was playing with my friends.