Orientate and conversate are examples of back-formations. Back-formations are words that have been created backward. Instead of starting with the root of a word and adding endings, people have started with a more complex form of a word and tried to remove endings to arrive at the root word. Sometimes this works.
For example, you could start from the noun hibernation and correctly derive from it the verb hibernate by changing the -ion to an e. Starting from the word orientation, people have mistakenly removed the -ion to try to get back to the root verb form of the word, but they have come up with orientate instead of the correct form orient. So many people have arrived at this word that it is now listed in the dictionary as a synonym for the word orient.
Orientate also has another, separate meaning: to turn toward the east.
Conversate is a newer back-formation. Webster's dates it as entering the language in 1973. It has no other meaning aside from being a synonym for converse.
Many back-formations are not considered proper words by usage guides such as the Oxford Dictionary of Usage and Style by Bryan A. Garner. Garner says that back-formations that are unnecessary because there is already a proper word for the concept are "objectionable."
Conversate and orientate are unnecessary synonyms for converse and orient, so do not use them in formal writing.
Here are other examples of back-formations to avoid:
