The best way to add an email address to your contacts is to ask the person you'd like to add to send you an email message.
Open the email in the Mail app. (I'm assuming that if you are using an iPad it is held vertically and that the email message fills the screen.) Explore near top of the screen for the email address of the sender. VoiceOver will speak "from sender's name, address, button". If you can't easily find the address then explore lower down the left of the screen to find any early part of the message and then swipe left to locate the address. Now double tap. You will hear "from, sender's name, address". It's a little odd, but you now need to double tap again. This brings up a menu that you can swipe right through or explore by sliding a finger over the men. You'll find both "create new contact" and "add to existing contact". Locate "create new contact" and then double tap. This brings up a partially filled contact information form. The first name, last name and email address should already be filled in. Swipe to check them and make any necessary changes. Finally swipe back left to the "Done, button" or explore near top right to locate it and double tap.
That's it; you've added that person to your contacts.
If you aren't using VoiceOver, all you need do to get to the screen with create new contact or add to existing contact is to tap on the from address twice.
If it isn't possible to get the new contact to send you an email, then you can add a new contact in the Contacts app.
Open the Contacts app; you could ask Siri to "open contacts". As usual, the app will start wherever you last left it. You will need to navigate to the page (or maybe panel on iPad) which lists your contacts and which is headed "Contacts", or possibly a service name like "Gmail" or "iCloud". Locate the "add, button" near the top right of the page or panel. Double tapping the add button takes you to the add contact form. VoiceOver will speak something like "text field, is editing, first name". Enter the first name using the on-screen keyboard, dictation or any other input method. If you used dictation then you can swipe right to the next field, Last Name, and double tap to begin editing it. If you used the keyboard VoiceOver will now be focused on the keyboard. Explore the screen above the keyboard by sliding your finger over the screen to find the last name field and then double tap to begin editing the last name using the on-screen keyboard or any other input method. Alternatively, find any field and then swipe left or right to locate the field you want to enter next and then double tap to begin editing it. Repeat this process until you have entered all the information you want to enter for this contact. Finally, locate the "Done" button near top right of the screen or panel and double tap to save your new contact.
If someone has sent you an email which includes the email address in its body or perhaps you have found the email address on a website you could use VoiceOver's advanced editing to copy the address and then paste it into a new contact. If you aren't using VoiceOver tapping and holding on the email address should bring up a menu which includes "create new contact" and"add to existing contact". Unfortunately, the VoiceOver equivalent of this, a triple tap, was extremely unreliable when I last checked this page in February 2025 and seldom works as expected.