Look at the tiles adjacent to the tribal capital. Choose a tile that produces resources you are interested in buying. Often these will be resources in short supply in your Empire.
Make sure your Merchant unit is selected and appears in the toolbar. Place your mouse cursor over the tile you picked. The cursor changes to represent some coins. Click on the tile.
The merchant moves to the tile and a dialog appears asking you if you want to pay the prices requested by the Tribe. This is a one time cost. To buy the land click “OK”.
