How to Activate an Apple ID?

What do you mean by activate? Is ti disabled?

If this is in the iTunes/App Store, see the 3rd link.

If your Apple ID is locked or disabled - Apple Support. https://support.apple.com/en-us/HT204106

If you have changed your ID or password, have you followed the steps in this article?

What to do after you change your Apple ID or password - Apple Support. https://support.apple.com/en-us/HT204071

If you see a message that says 'Your account has been disabled in the App Store and iTunes' - Apple Support.

https://support.apple.com/en-us/HT208856

If necessary, contact iTunes Support. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the

screens to get a chat or telephone option.

iTunes Store - Contact Us - Official Apple Support. https://support.apple.com/en-euro/itunes-contact

iTunes Support – world wide https://support.apple.com/choose-country-region/itunes

Are you seeing activation lock? If yes, see these Apple reads on activation lock:

Activation Lock for iPhone, iPad, and iPod touch https://support.apple.com/en-us/HT201365

Turn off Activation Lock https://support.apple.com/en-us/HT201441

If you can't activate your iPhone https://support.apple.com/en-us/HT201407

Go to here to choose a method of reaching Apple support (including by phone) https://getsupport.apple.com/?caller=kbase&PRKEYS=PF9&category_id=SC0068&symptom_id=20167

Note that Apple usually won’t unlock a phone without seeing its serial number on your purchase receipt. You may be able to take the receipt and the phone the to the genius bar (make an appointment https://www.apple.com/retail/geniusbar/) of a brick and mortar Apple Store for help in removing the lock.