On my Android, there is a feature that I can set password for app that I want to. Example, let's say I set a password for my gallery and then I install new app from play store or browser and the new app want to access my gallery. Can that new app access to my gallery?
No, The other app wont be able to access this app but other app can access this app data if its not stored encrypted on device storage. Other app only need storage permissions to do that. If other app can access device storage then that app can access any unencrypted data stored on device. But it wont be able to access OS files which are stored in read-only partitions/folder without having root access