We explicitly teach vocabulary and we use strategies to teach students to learn vocabulary on their own.
First, say the word (volcano). Then place your hand out and have the students repeat the word (volcano). Repeat this as needed to make sure there is correct pronunciation.
Second, give a definition of the word (a volcano is an opening, usually on a mountain or hill, that has molten/hot/liquid rock come out of it). Repeat the definition a few times depending on the looks on faces.
Third, use it in context or explain how it pertains to the lesson. (today, we are going to read about a volcano and how the molten rock comes out of the volcano).
And last, have the students turn and tell a partner the word and a definition for the word. As they are telling each other listen and observe to gauge their understanding.