Welcome to Android Central! You don't need an app to clear the app caches--on most phones, you can just go to
Settings>Storage, select Cached Data, and tap Clear Cached Data.
Lots of people use Clean Master, but I tend not to recommend it, because it seems to be associated with adware. I also caution against using these kinds of apps for "cleaning RAM," since that process is usually counterproductive in relation to how the Android system is designed to work.
Perhaps the best-regarded junk cleaning app that I've seen is
SD Maid. But I've never used it personally.