I can't use the sd card to download apps I just got a new phone but when I try to download something it says insufficient space but my sd card has plenty. How do I fix this?
Your SD card can be as big as possible, but Android won't use it. It's not safe for Android to assume your external SD card is always accessible.
Depending on your Android version, your internal storage is shared with your device storage i.e: Applications will not use less storage even if you move them to your SD card.