How do I get Custom Fields inside of a Page (not post)

I’m trying to use a plugin for my pages that requires me to enter a meta key:

– Create (or edit) a page to have a title of your choosing, and a parent page of your choosing (leave the content blank)
– Down below, add a meta key of “links_to” (without the quotes) and give a full URI as its value

How do I get custom fields to show up like they do in posts? or is there something else I’m overlooking?

Thanks!