One of the best side hustles is a virtual assistant. This can be done by finding someone who needs an assistant and then working for them on Fiverr or Upwork. You can make anywhere from $50 to $200 a day, depending on how much they're willing to pay. The downside is that you will need basic skills and equipment, so it's not exactly free money.
Tutoring online is another good side hustle. It can be done by tutoring on a site like Tutor.com or Chegg, and you can make anywhere from $10 to $100 a session.
If you want to sell products, then you should do something that involves affiliate marketing. You can earn anywhere from $100 to $1,000 a month with an Amazon Affiliate account, for example.