Welcome to AndroidCentral and thanks for the question 😃
Swipe down from the top of the screen once. (while on your home page). Tap the little cog icon on the top right hand side. This should take you into your settings.
Scroll down to storage (or something similar) and tap that. This should give a break down of the amount of space available on your Galaxy S6 and your Micro SD card. 😃
You may need to click on a button that says 'details' or something similar to that.
Hope this helps.
06-11-2017 12:29 PM