Install System App Remover (ROOT)
https://play.google.com/store/apps/details?id=com.jumobile.manager.systemapp
At first start, it will ask you for root permission. GRANT IT. If it is successful, you are rooted. Go to SuperSU and you will see permission logs, if the # symbol is marked in GREEN, it confirms the app for root permission acess.
Next, it is presumably your own understanding that rooting allows you to install/move apps to to SD card. You probably understand wrong on this aspect. Rooting is the merely first step, apps will always be installed by default into phone memory, so by rooting alone, your apps will still be installed into the phone's memory. You have to manually move installed apps into SD card, which can be done by the above app (SYSTEM APP REMOVER (ROOT)) - this is one of the key purpose of rooting.
As you move apps over to SD, you will free up phone memory which will allow you to install further apps. Just repeat the process as necessary, and be reminded that everytime PlayStore updates an app, even when the app has been previously moved to SD, the updated app will always be installed to phone memory as default. So you will need to repeat the moving to SD again after playstore updates to prevent your phone memory from becoming depleted.
By default, iirc, there is about 1.2gb free space thereabouts in the phone memory for apps at fresh state.