There are two ways that we use "in charge of ___". First, you can be "in charge of" a specific job or duty:

Eric, you're in charge of the food. Takeru is in charge of booking the DJ and so on.

Or you can be "in charge of" a person or a group of people:

When you're in charge of a team of over 30 people, it's pretty stressful.

In both cases, being "in charge" means that you are the leader or the person who's responsible.