It is basically a platform which acts as a middle-man between big brands/companies and normal people.
Companies pay Usertesting to get their sites tested by normal people and Usertesting pays normal people like me and you to test those sites after taking their commission.
Fiverr is a freelance marketplace where you can offer virtually any kind of service for at least $5.
There a lot categories on Fiverr. I would suggest browsing through them and selecting the ones that you can think you are good at.
Swagbucks is a survey and rewards site that has its own search engine.
When you search the web using their search engine, you earn free points which you can later cash out through PayPal.
There are many types of micro tasks available and you may not be able to do all of them so browse through them and only select those which match your skillset.