If I want to say what you(plural) forbid, how it would sound? The same?
Yes, that's right; Τι απαγορεύετε; "What do you(pl.) forbid?" would sound identical.
What would this be in the simple past resp. in the simple future?
"απαγορεύτηκε" resp. "θα απαγορευτεί"??
The υ confuses me. It sounds like a f, an i, an u, a v, and sometimes like an y.