도서박람회

어제 나랑 친구 함께 책 박람회에 가서요.
Yesterday, me and my friends went to a book fair.

어제, 나랑(와) 친구들은 함께 책 박람회에 갔었어요(갔어요). 

"My friends" is plural noun so you have to use "친구들".

"Went" is verb of past tense, so you must use "갔어요./갔었어요."

그것은 책을 너무 많아요.
There were many books there.

거기에 책들이 많았어요.

Many Korean people omit the subject word of sentence, and it's more natural, so you can omit "There".

"Books" is plural noun so you have to use "책들".

"Were" is verb of past tense, so you must use "많았어요."

책이 가 많은 종류가 있습니다.
There were many types of varieties there too.

또한 다양한 종류의 책들이 있었습니다.

"too" can be translated to "또한". and I already wrote about past-tense, plural noun related grammars.

하지만 그것은 심리학 책은 없었요 ㅠㅠㅠㅠㅠ
But they didn't have psychology books. TTTTTT

하지만 (그들은) 심리학(에 관한) 책을 갖고 있지 않았어요.  

=> It was translated literally about your English sentence.

하지만 심리학(에 관한) 책들은 없었어요. ㅠㅠㅠㅠ

=> It was translated literally about your Korean sentence.

Good-job! Cheer up! Have a nice day.