In one sentence, describe what the following article is about:

This is the three horizontal lines in the lower-right corner of your screen. It's at the very bottom of the page.      This email will be added to the list of emails that are linked to your Facebook. The remove button is located next to any emails that aren't your primary email. You can't delete your primary email without changing it first. You'll be brought to a page where you can tap on any of the emails you have on record to set that email as your primary. This is the email that Facebook uses to contact you if you have email notifications on, as well as the email you'll use to log into Facebook. After tapping on your preferred primary email, type your Facebook password into the box below and tap Save.

Summary:
Tap the Facebook app. Tap the menu button. Tap Settings. Tap Account Settings. Tap General. Tap Email. Tap Add Email Address to add an email. Type your email and password into the boxes provided. Tap Add Email. Tap Remove to delete an email. Tap Primary Email to switch your primary email.