To intubate is to insert a tube into something or someone. This is usually a medical procedure, so don't try to intubate someone at home.
See the word tube hiding in intubate? That's a clue that this is a word for inserting a tube somewhere, usually into a person for a medical purpose. Intubating is often performed on people who are having throat problems: the tube is inserted into the throat, allowing the patient to breathe. Other types of intubating may be used to feed a patient who is unable to eat.