If you combine two or more things or if they combine, they exist together.

If you combine two or more things or if they combine, they join together to make a single thing.

If someone or something combines two qualities or features, they have both those qualities or features at the same time.

If someone combines two activities, they do them both at the same time.

If two or more groups or organizations combine or if someone combines them, they join to form a single group or organization.

A combine is a group of people or organizations that are working or acting together.