FTSO stands for Flare Time Series Oracle, a system whereby a group of data providers are able to supply price data for other blockchains to the Flare and Songbird blockchains.
These submissions are rewarded, depending on a number of factors.
Price providers can vote on prices on behalf of others, so for example on Flare, you can wrap your coins into WFLR, which are 1:1 redeemable for FLR. The price provider takes a small fee for providing this service, usually less than 20%. Every time that provider provides data within an acceptable range, both the price provider and the person who they are voting on behalf of (delegating) will accrue a portion of the reward.
Over the course of weeks or months, this can become useful income for both the providers and those delegating. For a price provider these funds could be used to pay for infrastructure costs, whereas for someone delegating, they could spend it on a holiday, for example. Most of us just re-invest what we make, hoping for the big payday, the next bull run, or whatever.
The point is, if you're holding a bunch of FLR or SGB, you can make it work for you, risk free, on a low carbon blockchain. Making a few extra $ doesn't have to cost the earth!