There's a difference depending on whether you're talking about a physical one or a virtual one. If you're in Rome, arranging to meet someone, you would say "I'll meet you at The Forum at 3pm". If you're arranging to be online here at the same time as someone else, you'd say "I'll be on the forum at 3pm. See you there".
Your question should have been "What do we need to say?" We've told you this before.