Many battlefields have Victory Locations (VL) on them, which grant various advantages to their owner.
To capture one of these, simply move a unit near the VL, within the circle that is displayed when you hover the cursor over the VL. As your unit begins to capture the location, a Capture Bar is displayed next to the VL flag, which slowly fills up. When the bar is full, the VL flag will change to your colour on both the battlefield, and the minimap. Note that enemy units within a VL circle will prevent you from capturing that VL.
If the VL grants a useable ability, it will appear on the left edge of the Minimap Frame.