Commander, you are able to send an army anywhere on the map regardless if it's an occupied spot or not. Using your army Supplies you can selecting an empty spot on the map and send units there to camp for a limited amount of time. The further you send your troops the more supplies will be consumed. Once all supplies are exhausted the army will automatically return home.
When sending armies you can chose the point of departure, your home Base or all available camps around the map. If you decide to perform any action with any of your camp, this will consume all their Supplies and after that action is done the remaining troops will return home. You can have a maximum of 5 camping armies. Each camp will gets a specific name for you to recognize them: Alpha, Bravo, Charlie, Delta & Echo. To send one of your camping armies onward, choose a target on the Map and from Send Army screen pick the appropriate camp for that action. Selecting that camp will display all troops that are currently in and the remaining supplies. From there it's just a tap away to send your camp to it's new target or destination
However you can not change or resupply any of your already existing camps, nor split one in two. If you wish to do so first you should get your squad home and send them out again. Each march starts with a fresh number of Supplies automatically.
TIP: Camps are good way to reserve spaces, hide troops or even sneak attack some far away opponent without them realizing it. What else will you use them for Commander, is up to you.