The first day of my summer holiday

Today is the first day of my summer holiday. (Always capitalize the first letter of the first word in a sentence.)

I'm a chinese girl and now study in college. (You need an apostrophe when using contractions. Use 'a' instead of 'an' when the next word starts with a consonant.)

I like sports, especially swimming. (Always capitalize 'I' when used as a pronoun.)

I like dogs, traveling, and eating nice food. (Dog should be plural since you like more than one or you need to be specific as to which dog you like. Add, -ing to eat for the present participle form.)

I have a boyfriend 5 years older than me. 

We met for two years ago and 14 days later was Chinese Valentine's Day, so I was very except excited it. (This sentence is difficult. I assumed you met your boyfriend 2 years ago and that Chinese Valentine's Day was 14 days later. The next part of the sentence I am unsure of so I indicated you were excited about the circumstance.) 

I hope our my friends will be happy and I hope know to make many new friends here. (Typically, we make friends or get to know people.)

I removed some commas and made short sentences. They are easier to read and understand.

I hope this helps.