So pretty much you can attack other players bases/lands by swiping right on the land your army is currently stationed at, and select the big yellow button that says army controls. Once you are in that screen it will show 3 options, move army, attack lands, and attack bases. If you wanted to attack someone's lands (any captured points in your own bases radius not including the enemy players base) you just need to select the attack lands option and then a popup window will appear with all the list of players in your vicinity. If there is noone near you, you will get a message saying exactly that. If you wanted to attack someones actual home base, you would just select the attack bases option and it will show you the bases in your radius. The comment about not being able to choose who you attack is if you have a guard tower at your base, you can attack all the lands that are in your bases small radius that you see when you zoom into your bases location. That's really the only time you can't choose who you attack. Hopefully this helps 😎