Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
Sounds like the internal storage is full. So you have to either delete some unwanted photos, videos, music etc or you have to move your files to SD card.
Open My Files app. Tap Photos or tap Videos (better to move videos). You will see folders or video files there. So select them, then tap the 3 dots at top right and tap Move. Select SD card. This will move them to SD card.
Do the same for all other files that you would like to move to SD card.
Let me know how it goes.
Where is My Files app?
You should see it on the home screen. It should look like this --> http://careace.net/wp-content/uploads/2011/09/my-files-application.png
You can also use third party File Managers to move folders from Internal Storage to SD card. Open Play Store, search ES File Manager and install it. Then you can use it to move stuffs to SD card.