As a call center agent you will either get calls automatically or you'll get them when you are logged in and available. This is set by the admin.
You can see a call coming in from a Call Center on your telephone with the name of the Call Center, Like "Customer Service" or "New Sales."
Simply answer the call, but picking up the handset or pressing headset.

If you login to the call center, you will have softkeys that are SignIn, SignOut, Available, Unavailable. You should SignIn & Available when you are ready to take calls. If you go on break you should Select Unavailable. And when you go home at the end of the day, SignOut.