I did not capitalize aquarium as it is a generic name. If it the actual name of the place (Like the Louvre) then it would be capitalized.

Last weekend, I went to the aquarium with my friends Jane and Tom. We had a very good time looking at the dolphins and the whales. Did you go to the aquarium before? You must to go; it is real amazing. It was my first time, but I want to go again because their are so many things to see.

Last weekend, I went TO the Aquarium with my FRIENDS Jane and Tom. We had a very good timeLOOKING AT the dolphins and the WHALES. HAVE YOU BEEN to the Aquarium before? You must to go; (NOTE SEMI-COLON HERE) it is real amazing. It WAS my first time, but I want to go again because THERE ARE so many things to see. (PERIOD AT SENTENCE END)

“to the aquarium” — is the active form; using “at” implies you are already there, it implies passive tense.

“looking at the dolphins and whales” – to look is the wrong tense; looking at is the correct form of the verb. whales is the correct spelling, not wales.

“Did you go to the aquarium before” — again the verb tense has to match the present tense; went implies the past tense.

You must go, it is real amazing; again the verb tense is wrong — to go is not correct english

It was my first time — only one person so was is the correct tense of the verb.

because there are so many things to see — there is the correct word here “their” is a possessive pronoun.

are so many things — use “are” to match the number of things to see.

hope this helps you…

replace preposition “at” with “to” & make “friend” plural by adding “s”

Second sentence:

delete preposition “to,” add -ing to “look” and insert preposition “at” // correct spelling of “whales” by inserting an “h”

Third sentence:

Replace “Did you went” with “Have you gone”

Fourth sentence:

Delete preposition “to” & insert verb “go // change adjective “real” to an adverb by adding -ly

Fifth sentence:

Change verb “were” to “was” // change pronoun-verb combo “their is” to adverb-verb combo “there are” & add period to end sentence.

The corrected paragraph ends up looking like this:

Last weekend, I went to the Aquarium with my friends Jane and Tom. We had a very good time looking at the dolphins and the whales. Have you gone to the Aquarium before? You must go, it is really amazing. It was my first time, but I want to go again because there are so many things to see.