Processing verbal information into your knowledge system is the input side of verbal fluency. The output side is generating verbal information from your knowledge system. Fluency is partly the ability to understand what you read or hear, and it is partly the ability to express your understanding in writing or speaking. Although in general, the better you are in processing verbal information, the better you are in generating verbal information, they are not quite two sides of the same coin.
The steps required to generate verbal information are the same as processing verbal information except in reverse order. That is to say, you start with the idea, code it into words, and ultimately you organize the words into meaningful sentences. But just as most people can't even spell their name backwards very fast (can you?), most people can't generate sentences about complex ideas nearly as rapidly as they can read them. In both cases, sufficient practice with the backward order leads to fast, automatic performance. However, recall that you learn what you practice. Thus, if you have practiced generating ungrammatical sentences, that is the kind of sentence you have learned to make.