i was go to the bookstore yesterday

after leave the office, i was drop in samsung station.
there is coex, trade center, department store and so on.
inside coex, Bandi&Lunis located.
i was look around generally. but did not buy the book
but always fun when i go to the bookstore

instead of "I was drop in," you could say "I stopped by" or "I dropped by"

add the "-ed" to identify the verb as past tense to say I did this.

I was go went to the bookstore yesterday.

After I leave left the office, I was drop in went to Samseong Station.
there is The Coex, trade center, department stores and so on more are located there.
Inside Coex Mall is Bandi & Luni's Bookstore. located.
I was look browsed around, generally but I did not buy the any books.
but I always have fun when I go to the bookstore.

Remember to capitalize at the beginning of sentences and proper nouns and your punctuations. Be careful not to mix your tenses.