This video is a great explanation of how user testing from your computer works with UserTesting.com. This concept is similar for other companies that ask independent contractors to perform user testing.
To sign up, go to https://www.usertesting.com/be-a-user-tester and get started!
A small list of vetted companies that pay independent contractors to test the user functionality and experience of various websites, applications, etc. Please allow time for the email to be sent to you, but if you do not recieve within 24 hours, please send an email to firstname.lastname@example.org