What happens when you try? Error message(s)?
Have you tried signing out of the App Store/iTunes, restarting the device, and then signing back in?
See the Apple Support article(s) below.
Apps won’t downloaded.
App Store, iTunes Store, or other Apple services - If you can't connect
Some things you can try. Do you have access to another WiFi network where you can try? That has worked for several people.
Try a restart.
Restart your iPhone, iPad, or iPod touch
Try a forced restart.
Reset Device.
If necessary
Hard reset.
Do a backup and try a factory reset. Then restore from your backup.
Restore to Factory setting.
Backup - Restore your device from an iCloud or iTunes backup.