Command Query Responsibility Segregation is a simple concept. When you want something to happen, you will use a Command. If you need results returned, you will use a query.
An over simplified example of this would be if you need to write to a database, you would use a Command. If you need results from a database, you would use a Query.
Installing the Symfony Bridge will add additional functionality to the CQRS component. This can be done quickly and easily. The documentation will point out where this is required.