My essay

I started learning English one month ago, and my teacher said that we must write an essay about something that we like, so I'm going to write about tennis . In my country, tennis is not a very popular sport, most people prefer baseball or soccer. I usually go with my family to the stadium and we see many baseball games, but I didn`t see any tennis matches (because here our athletes have not qualified for the Us Open or Australian Open). Nevertheless, I always have seen it on tv. 

I have loved tennis since I was eighteen years old.  While at  my grandmother's house, it was  just my sister and I bored in front of the tv. Soon we started to watched a game, now my sister and I always watch the game together.

My essy

Please note, comments are inside {}

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I started {"started" is past tense} to learn English one {"one" is acceptable, American English may just use the article "a"} month ago, and my teacher says {depending on meaning, should be "said" or "says" - if this is past tense then "said", if the teacher is saying to do it now then "says" which is the plural conjugation, said is most likely what you want} that we must writte {spelling, should be "write"} an essay about something that we like, and I going to writte about tennis because I {after "because" you are starting a new phrase and should specify the subject of the phrase} like this sport. In my country tennis it'sis {word choice, would not say "it is" only "is"} not a very popular game, the people preferdprefer {the people still do, prefered would be in the past} baseball or soccer,. {starting a new idea, full stop with period not comma} I was with my family toat {Word choice} the {specify article, it is expected}  stadium and we seesaw {word choice, you started in the past tense with "was with" so this implies you watched/saw/"to see" in the past as well} many baseball games {many implies the noun should be plural}, but I did`t sawdon't see {there is no contraction "did't" there is "didn't" which is  combination of "did not", however the action of not seeing is in the present tense, thus "I don't see"} tennis games {when refering to them in general, implies multiple games and thus plural} because here there are not champions aslike {word choice, "like" and "as" can sometimes have a similar meaning, but like should be used here} Us Open or Australian Open, which {connecting word to join the phrases} I always havehave always seen inon {word choice, on is the proper word here, "in" implies inside the tv- we consider the image to be on(top) of the outside of the TV} tv.
 
I have loved of {unnecesary} tennis when was since I was {use present tense, since you still love it} eighteen in my grandmother's house {it is unclear what you mean here, perhaps you want to say "I have loved tennis since I was eighteen and first saw it at my grandmother's house"}, I was only with my sister and we waswere {first person plural conjucation} boried {spelling} and start to {you can either says "started to watch" or just "watched", saying only "watched" is better} watched a game, now my sister and I will always watch thea {word choice, use "a" since you are not talking about a specific game} game together.