You can answer a call when you're already in another call. Call waiting is a network service.

Select Answer key icon. The first call is put on hold.

Switch on or off, or check the status of the service

Select Settings and Calling > Call > Call waiting > Activate, Deactivate, or Check status.

Swap between an active call and a call on hold

Select Options icon > Swap.

Connect the call on hold to the active call

Select Options icon > Transfer. You disconnect yourself from the calls.

End an active call

Select End active call icon.

End both calls

Select Options icon > End all calls.