What is "Metalanguage?"
When English language teachers (and other languages, too) talk about "metalanguage," they primarily mean the "language" used to talk about the target language. A simple example would be if I say "present perfect progressive sentence" to talk about the form and functions of a sentence like "I have been studying English since I was a child."
Using metalanguage is an easy way for teachers (and others) to talk about a language. It's not a great idea to use metalanguage to teach English language learners. It's better to go directly to the target language. For example, if I'm teaching the Simple Present, I would use and elicit the target language. I might ask, "What do you do every morning?" In this case, I am hoping to get something like, "I eat breakfast." I am using the Simple Present, rather than talking about the Simple Present.
I do use some metalanguage when I am teaching advanced ESL students. They usually know all the names of grammar parts, and so it saves a lot of time to use the shortcut of metalanguage.