When working through emails in your inbox, wen you either archive, move, or delete an email leaving the "Auto-select Next Conversation" option checked will do just that, otherwise you can manually select the next conversation in your inbox or folder.
To change these settings:
1) Go to Mailbird menu in the top left of the main window
2) Select "Settings"
3) Click the "Advanced tab"
4) Check or un-check "Auto-select next conversation when archiving"