After you have finished attacking, you can fortify armies.

Click the Fortify button.

You can move armies between adjacent countries that you own.

Click a country to select it.

When you select a country, its armies are shown in the armies drawer.

You can then place armies in any adjacent country, or back in the selected country.

Each army can only be moved once per turn. Armies that have already moved are not shown in the armies drawer.

When you are finished, click the Done button.