How do I Activate my keybord for my tablet?

Go to settings of your tablet, and see if the keyboard is there, tick it to be your default keyboard.
else, you can also do this, tap message application, tap new message, tap the gear like button next to space bar at the left side of it, do note that sometimes, instead of the gear like button, it shows smilies or symbol, long tap it and it will lead you to your keyboard settings and tick your bluetooth keyboard.