Garrisoning lets you store units in buildings or other units. Sometimes, nifty things happen.
Units heal while they are garrisoned in buildings. Infantry and Cavalry units garrisoned in fortresses, warships, or civic centers increase the number of arrows fired. Defense Tower can be garrisoned by Infantry and support units but not Cavalry. Units garrisoned in Temples heal faster than any other building type.
Land units can be transported across water by garrisoning them inside a ship. You can garrison Traders in Merchant Ships to increase the ship's Gain. A support or Infantry unit garrisoned in a Fishing Boat increases its fishing rate.
How to garrison
To garrison a unit inside a building or a siege unit, click the Garrison button in the menu or simply hold Ctrl button. The cursor will turn into garrison icon. Then click the target building/unit. If a building or unit can be garrisoned the cursor will display the amount of units already garrisoned in it. Otherwise the garrison icon will turn gray.
To ungarrison the unit click the building/siege unit and click the unit displayed in the profile to ungarrison it. To ungarrison all unit click Unload All button in the menu.