Why my password don’t work for my iTunes download

Is this when you are trying to sign in or when you are trying to update an app?

A request for another Apple ID password is often caused by updates to apps/purchases that were made when using the other ID. Those purchases are tied to the other ID and can't be transferred. One option is to delete the apps/purchases made by the other ID and download them using the new ID if desired. If necessary, check your purchases history to see which apps/purchases weren’t made by the current ID. 

Purchase History Review.   

Are you signing into Settings/iTunes & App Store? Does the ID and password work other places?

 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.      

When my phone was set up by a person who literally drove the phone to me (via APPLE contractor) we had trouble setting up my user name and password. She finally left, unable to do more because it turned out that while I was employed as a school district of Phila. teacher, the computer lab person set up our teaching computers including passwords. These were not given to us. After years of service as a teacher, I retired 5 years ago, and all computers were changed and / or updated. I have an adult son who helped set up my user name and password. I never used it for the i-tunes or app store, until I had to sign in for a virtual doctor's appointment. My password failed repeatedly. I changed it following the manual instructions, and it was verified as going through correctly, however, I still can't sign in without it repeatedly saying failed and "your user name or password is incorrect". I don't know what to do.

I can’t sign in to download any app with my Apple ID. It says it has not been been used for iTunes yet and it has not been used yet because I just bought this iPhone se. I would like to down load Facebook and messenger. I am disappointed never had problems before with apple