"Revocate" means to call back, recall. For example, to send a message to troops to retreat. I have an excellent vocabulary, but was previously unaware this word existed, so I think it's reasonable to assume its use will usually raise eyebrows among even very fluent, well-educated speakers — most of whom will assume you misspelled "revoke". Some dictionaries mark it as obsolete, and I'm not surprised.
"Revoke", on the other hand, is a fairly common word, meaning to undo a previously-valid decision or law. For example, to cancel a previously-granted permission to do something.
If you want to use revocate, you should seriously consider simply saying "call back" or something similar instead. Even in formal uses, this will likely be the best choice; borrowing from the previous example, a military text that mentioned a general "recalling" his troops would be perfectly natural, while one that mentioned that general "revocating" his troops would be hard to understand.
"Revocation", itself, has nothing to do with "revocate", other than by etymology. It's the noun form of "revoke". So one might refer to "the revocation of an order", meaning its cancellation.