First, let's have a look at the ISO/OSI stack vs the TCP/IP stack:
ISO/OSI layer 5 is not much "used" alone: it is implemented together with layers 6 and 7 to the TCP/IP Application layer, where network applications such as HTTP, NTP, IMAP etc. take place. In practice, its functions are mixed with the upper layers.
The session layer controls the dialogues (connections) between computers. It establishes, manages and terminates the connections between the local and remote application. It provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. The OSI model made this layer responsible for graceful close of sessions, which is a property of the Transmission Control Protocol, and also for session checkpointing and recovery, which is not usually used in the Internet Protocol Suite. The session layer is commonly implemented explicitly in application environments that use remote procedure calls.