Please help me to understand

Hi,

please help me to understand why this sentence incorrect: "I saw him yesterday..the correct sentence is " I didn't see him yesterday."

Both of these sentences are correct grammar.
I saw him yesterday.
I didn't see him yesterday.

Yes, both of sentence are correct, the first one is positive pastence and the second one is negative pastence

Anonymous, the term "past tense" is two words.

"I saw him yesterday" and "I didn't see him yesterday" not have same meaning

I have a question too, but is "it" a preposition?

pls ask, lets chat

Hello anon;
Please post your question only once.

And no, it is a pronoun.

eg.

Close the door. Just give it a push.
That is a good dog. See, it's (it is) wagging its tail.
When you post, use polite words like please and thank you. It is the right thing to do.

Anon is not buying it.lol

guillotine Anon is not buying it.lol

Sometimes it's a challenge.

Anonymousplease help me to understand why this sentence incorrect: "I saw him yesterday..the correct sentence is " I didn't see him yesterday."

Anon,
I tried to understand how you perceive this question which you called incorrect. It baffles me! Perhaps, you need to give your re