Snap the extra edges off the board by first bending back and forth a couple of times. Identify the component side of the Expansion Board which is clearly marked HB Expansion Board.
Most components sit on the component side, with their leads poking through to the solder side.
The board is then soldered from the solder side. The exceptions are the six servo headers. These male header pins mount facing down from the bottom of the board. Installation instructions are provided to remind you that these are mounted down from the bottom of the board. So unless otherwise noted, when installing a component, assume that it is mounted to sit on the component side of the board.