A session is a way to preserve certain data across subsequent accesses. It can be set up at a certain point in time and implemented later. When converting files, you can save its current state as a Session. The current state consists of the files added for conversion, the status of the files (Pending, converted, aborted, failed) and the conversion settings such as the audio and video properties.
Creating a session lets you set up a project and save it. You can work on something else (or shut off the computer) and return to your session later.
It may be the case that you have split a media file and added the segments to the conversion list. These segments are preserved in the conversion list when you create and save a session.
To create a session, add files for conversion and click File >> Save Session. Your session is created with the filename that you specify and an extension ".dmc". It is saved at the location that you choose.
At any point you can open the session and resume the conversion where you left it. Click File >> Open Session, navigate to your .dmc file and open it. When you make any changes in the current session, you will be prompted to save them.
To start a new session, close the current one by clicking File >> Close Session. When the current session is closed, you can start adding files for a new session.