Not sure why yours is asking you to select the hub every time (it should remember and only change if you log out of the app), but you don't really need the app to control devices. The "Devices" tab in the mobile app is supposed to make this easier (but again, probably not if you have to select the hub...), but Hubitat Dashboard is a built-in option that allows you to view and control devices. The app provides easy access to it (though again, probably not if you have to select the hub...), but they are just webpages you can bookmark. The "child app" for your particular Dashboard (again, the child Dashboard app in the admin UI, not the Dashboard itself) will have the link. I'm not sure what it was suggested to bookmark above, but the Dashboard will probably be easier to turn on/off things than the admin UI. You just have to set it up first. But the admin UI will work too if you don't mind that interface.
Or...you can find some way to automate this. (Motion sensor? Time of day? Maybe a remote/button device?) If you have to pull your phone out to turn on or off lights, it's just a really expensive, cumbersome light switch. There are a lot of ways a hub like Hubitat can help you make this a smart device and not a more annoying one. You can find lots of ideas here, or perhaps someone can suggest something if you have any ideas.