Can I paste names in instead of uploading a file?

Yes. Open Import and paste your list into the box under the file drop, one guest per line. A line with two words becomes a first and last name; a line with an email address keeps it.

Pasting is the quickest way in from a note on your phone or a message. For meals, groups or tables, a spreadsheet with those columns is better: see What columns should my spreadsheet have?