When you run DBConvert / DBSync application for the first time there is no Sessions stage available as there are no sessions saved yet.
Since then every time you launch the program there is an option to run a session you saved previously. Select the name of the session you'd like to run from the list of saved sessions that drops down after clicking on the combo box arrow. Unnecessary sessions from the list by clicking on "Delete" button nearby (X).
Information about source and destination databases configuration is displayed in the corresponding group boxes.
New > - In case there are no saved sessions you can configure a new session click "New" button that brings you to the step called "Choose Source" where you can start configuring settings for a new migration process.
Load > - All necessary information for converting your data (source, destination, settings) will be loaded as it was specified in the selected session so you only need to make changes where needed.
Execute > - Clicking at "Execute" button loads selected session and brings you to the last Execution step to launch migration and watch the operation log.