Agree with- एक व्यक्ति से सहमत।
Agree with a person
I totally agree with you Vandana.

Agree on- बात या निर्णय पर सहमत होना।
Agree on matter or decision.
Let us agree on the 20th of this month.

Agree to- एक सुझाव के लिए सहमत हैं।
Agree to a suggestion
We agree to your proposal.