Correct this:

i love ice cream it is the best treat in the world

I love ice cream. It is the best treat in the world!

Capitalize the first letter in every sentence, and always put a period or exclamation at the end of a sentence if it is a command, or an exclamation.

Well,

First, you should capitalize the first word of each sentence.

I love ice cream it is the best treat in the world

Now, obviously we have to put punctuation somewhere in the middle of the sentence. We could put a period, a semicolon, or an exclamation mark after the word "cream." For the punctuation after the word "world," we could put a period or an exclamation mark.

I love ice cream. It is the best treat in the world.

I love ice cream; it is the best treat in the world.

I love ice cream! It is the best treat in the world.

I love ice cream. It is the best treat in the world!

I love ice cream; it is the best treat in the world!

I love ice cream! It is the best treat in the world!

Different punctuation will produce different effects. For example: the first sentence had the least excitement, while the last sentence had the most excitement.