I agree or I'm agree

Spanish speakers usually say I'm agree. In Spanish, the equivalent expression is "Estoy de acuerdo". Agree is not a synonym of "de acuerdo". Agree is a verb. It means: estar de acuerdo. Thus, the right way to use it is:

I agree (with you).

I don't agree with you or I disagree with you.

I disagree with you on the plan.

For more examples, see agree - dictionary