This is how you handle incoming telephony in ACE Agent.
The Answer button flashes when a call has been routed to you.
The Answer button, the F2 key on your keyboard, or the Contact handling |Answer menu choice answers calls unless you have already, in Client settings, specified that contacts shall be answered automatically.
Never use the telephone to answer, as the call may then not be registered as answered in ACE. Only exception is if you work in Light Mode. Then you have to use the telephone as well. See Handle phone calls in Light Mode and Settings for Light Mode users.
When a call has been answered, several buttons become available. Exactly which buttons, depends on the current status of ACE Agent. ACE Agent.