This method is the Coinbase "Rewards" program. With the "Rewards" program you can watch videos about different cryptocurrencies and earn a small amout of the coins, which can be traded into BTC.
This guide includes the AMP, The Graph(GRT), Clover Finance(CLV) and Fetch.ai(FET) coins, because this was the only coins aviable to me at this point of time, but in the future more coins will be available.
You only have to watch some videos about the coins and answer some questions about the coins. In total it is only 13 minutes of videos to earn 13 USD.
To do this method you need a Coinbase account. If you don't have that it is no problem, you can just create one.
Before you can watch the videos from the "earn" program, you have to verify your account and be elligable to earn coins.
It only took 2 days for me from signing up to beginning to earn, but if you are already verified on coinbase you can start immediately.
Link to the Coinbase "Rewards" program: https://www.coinbase.com/rewards (Non affiliate)
AMP
With the "earn" program you can earn 3 USD worth of AMP for 3 minutes of video watching.
GRT(The Graph)
With the "earn" program you can earn 4 USD worth of GRT for 4 minutes of video watching.
CLV(Clover Finance)
With the "earn" program you can earn 3 USD worth of CLV for 3 minutes of video watching.
FET(Fetch.ai)
With the "earn" program you can earn 3 USD worth of FET for 3 minutes of video watching.
All of these coins can be converted to BTC, ETH or any other coin that Coinbase support without any fees.