After setting up your first connection through Welcome Screen, you will see the Connection List every time you click on Start.
In this screen, you can connect to existing connections, or manage your connections.
From the Connections List, you can click on Connect to login to the respective environments. If your session has expired, enter you Salesforce credentials to login again.
You can also mark the connections that you use frequently to Auto Connect. These connections will automatically connect the next time you click on Start.
Click on New Connection on the top right and choose the CRM you want to connect to. Give your connection a descriptive name, provide the Login URL, and login screen for the selected CRM will pop up for you to login.