I helped my mother wash the dishes.

I helped my mother clean the house.

I helped my mother ironing some clothes.

I vacuumed the floor.

I cleaned the floor with a mop.

I cleaned the study which was messy.

I cleaned the veranda where there were a lot of items such as books, audio tapes, etc.

I wiped the floor of the dining room with a broom and a dustpan.

I helped my mother do the laundry.

I helped my father clean the car.

I watched a soap opera on TV by myself.

I did my math homework.

I did three kinds of homework with my friends.

I went to one of my friend's house and played computer games there.

I went to a PC room and played Star Craft with others on line.

I went to a singing room to enjoy singing with my friends.

I went to a billiards room to play billiards with my close friends.

I went to my friend's office and ate jajangmyeon together.

I went to my friend's factory and had dinner together after he finished his work.

(Would you check the sentences? Are they all grammatical? Thank you.)

I helped my mother iron some clothes.

(iron not ironing)

I went to a PC room and played Star Craft with others online. (online should be one word)

I helped her wash the dishes

I think it should be "Are they grammatically correct?''

rather than ''Are they all grammatical?'' but I might be wrong, English is my 2nd language

Yes, all of the sentences you provided are grammatically correct. They are written in the past tense and each sentence is complete with a subject and verb. The sentences also express a clear action or activity that you performed or participated in. Overall, your sentences are well-structured and convey your actions and experiences accurately.