If your microSD card is new or doesn't have content you want to keep, you can set it up as internal storage for your phone. Your phone needs to be running Android 6 Marshmallow or higher. This helps to expand the phone storage space since you can migrate apps that you installed and their data to the card. One important reminder, though, is that after setting up the microSD card as internal storage, the card can only be used on the phone where it has been formatted. You won't be able to insert and access the card on other phones.
See the user guide or how-tos to find out how to set up the microSD card as internal storage.