Hide files or folders without any app

Step 1. Every Android has file explorer in it, but if you don't have any, I recommend you to download Es File Explorer on your Android device. Now open your file explorer.

Step 2. Now select your file or folder which you want to hide from others.

Step 3. Now select the file or folder and click on rename option. then add there a "."(Dot) at the start of the name. 
(For example if the folder is videos then rename it as .videos)

Step 4. It will hide that file or folder that you renamed. Now if you want to open that file or folder then just select show hidden files option in your file explorer

Step 5. If you want to make that folder unhidden then just rename the file by removing "." (Dot)from the name.