To express agreement in Engpsh, you can use phrases such as:
"I agree."
"I concur."
"I'm in agreement."
"I support that idea."
"I'm on board with that."
For example:
Person 1: "I think we should go out to eat tonight."
Person 2: "I agree. Let's try that new restaurant downtown."
Person 1: "I think we should start the meeting at 10am."
Person 2: "I concur. That time works for me."