The session layer performs the following functions:
Communication with the Presentation layer above.
Organize and manage one or more connections per application, between hosts.
Communication with the Transport layer below.
The overall communication itself is know session.
An example application is web conferencing, in which the streams of audio and video must be synchronous to avoid so-called lip synch problems. Floor control ensures that the person displayed on screen is the current speaker.
Another application is in live TV programs, where streams of audio and video need to be seamlessly merged and transitioned from one to the other to avoid silent airtime or excessive overlap.