The manager is someone who will serve as your guide when you are doing the things that are important for your career. The manager will be in charge of making sure that you have enough time to do all of your required tasks. The agent will be in charge of your contract and will also try to find the gigs and work that will allow you to have the money that you deserve.
They may also be in charge of doing the negotiations for you because this may be something that they are good at. The manager may be the person who will help you find the right agent to help you jumpstart your career.