A script might help.
There will be an expanded version of this piece in an upcoming book (due in a few months), but I see the need for this understanding now. The phrase "Use your words," is very common from adults working with young children. It is usually in response to a conflict among children or in response to some unacceptable behavior. The hope among the adults is that the child will say, "Can I please have a turn." Rather than snatching a toy or bopping a peer on the head to get what they want. The hope is that the child will generally use language rather than some kind of aggressive or tantrum-like behavior. It's great advice and guidance IF the child has the words. Saying "use your words" assumes that the child has them, but in my many years of working in schools I've found that this is often not the case. Or they may have the "wrong" words.
Children don't automatically develop effective communication skills. They need guidance and sometimes very explicit training. Even older kids often benefit from developing effective scripts for a variety of situations. In my work with children individually and in classroom discussions we generate and practice a number of scripts to deal with a range of experiences. Some of the common scripts are for ways to express a request such as, "Can I have a turn with that toy." Or to set boundaries on a peer with something like, "I don't like it when you pull on me, please stop." Even the script for a proper apology is useful and can include many parts. An elaborate version might be something like, "I'm sorry I did that. I didn't mean to hurt you. I'll be more careful from now one."
So when we ask them to use their words, it a great idea to make sure that they have those words.