File management on Android is improving, but it's still not great, and it can be frustrating trying to take control of exactly which files are saved and where they're stored. Numerous third-party apps have rushed in to fill the gap but one of the best we've seen in recent times is Cabinet -- it's fast, feature-rich and a signed-up member of the Material Design club.
The app is still technically in beta but it's still very usable. As you would expect you can move, delete and rename files as you wish, and there are some powerful search and filtering tools to take advantage of. You can get into the root directory if needed and there are quick links to the pictures, music and download folders (the latter is a good place to start if you want to tidy up your device).
You can access details of each file, open obscure file types like ZIP, and preview the common formats from right inside the app too. External storage devices and remote connections are supported. Use the familiar button in the lower left corner (found in many a Material Design app) to create a new folder or file in the current folder.
Cabinet adds itself to the Share menu within Android, and if you pick the Save to... option from the list you can use Cabinet to save files from the web (or anywhere else) to a folder of your choice. It's a useful option to have if you want to take more control over where your data is. Finally, if you don't like the default theme design, you can change the colours around through the app settings.