It involves the teacher first modelling a word or a sentence and the learners repeating it. The teacher then substitutes one or more key words, or changes the prompt, and the learners say the new structure.
Example
The following sequence is an example of a substitution drill:
Teacher: I have a new car
Learners: Have you?
Teacher: I don't like fish
Learners: Don't you?
Teacher: I love coffee
Learners: Do you?
In the classroom
Despite a move away from drilling as a classroom technique, many teachers still use it to provide practice. One way to move a drill away from being teacher-centred is to ask a learner to lead the activity.
Further links:
https://www.teachingenglish.org.uk/article/drilling-1
https://www.teachingenglish.org.uk/article/drilling-2
https://www.teachingenglish.org.uk/article/drills-are-back-fashion-now-taste-style
https://www.teachingenglish.org.uk/article/teaching-structures-situations