Use command as a verb. This will refer to an action of giving an order, leading, or demanding. In most cases, this means it will come after the subject, who will be doing the commanding, but before the direct object, which is the person, people, idea or other entities under command.
Example: Leaders like President Lincoln command a great deal of respect because of their integrity.
Include command as an adjective describing a noun in the sentence. This will refer to an object that has to do with carrying out a position of seniority, or with handling duties made necessary by an emergency or by order from the head of a government.
Example: The general made all of his decisions from the central command post.
Use command as a noun. This will refer to the order given, the act of givng an order, specific groups of soldiers, or a particular ship, submarine or other posting station.
Example: The general gave up his command when he retired.