Michael, Here is a corrected version: "Last Saturday I woke up very early in the morning. I brushed my teeth and washed my face. I cooked and ate breakfast at home. Then I went to the library. I usually go to the library at 8:30AM, but last Saturday I went at 8:00AM. The library was very crowded. I stayed there all day. I got home at 5:00PM. So, what did you do last Saturday?" Please let me know if you have any questions.

Let me help you. Last Sat(abbreviation of Saturday surely),I got up pretty early in the morning,brushed my teeth and washed my face. I cooked & had breakfast on my own and went to the library. I often go to the library at 8:30AM ,but last Sat I went to the library at 8:00AM. The library was so much crowded. I stayed at the library all day. I returned home at 5:00PM. So,what did you do last Saturday ?(About this sentence,you could also say this way How was your last Saturday?) In case you want to strengthen the meaning of an adverb,please do not use so much. Instead of it,they use pretty,suprisingly,etc in America. Just a little showoff of Native American English. Hope you good luck with your future learning. Best regards From kind Jay K.

thanks a lot.

This is not the section for corrections. You want the 'notebook' section. Before you do that though, can I suggest you learn how to punctuate correctly? For some reason, most Chinese teachers fail to teach this to students. You need one space after punctuation marks, and no spaces before them. Fix those up, and save the person that corrects your writing from doing it for you. See how I have (hopefully correctly) done it? Can you see how every literate European does it exactly the same? It does matter, and makes your writing hard to read if you are used to seeing it done correctly. You also need 'the' before all your 'library's.