Technically it’s running a proof-of-stake stake pool and using the operational rewards to fund CI hardware for GHC. It currently provides 7 Linux, 2 windows and 3 m1 macs as well as covers the maintenance for them.

Thus by staking ada (cardano) with the stake pool, one can “earn” a competitive rate (~4%) of stake return as well as support GHCs CI indirectly as the excess operational rewards from running the pool are put towards running CI machines for GHC.

To compare this to some non-blockchain scenario:

Depositing money at a bank will yield some interest, but also provide the bank with some operational return (they usually don’t provide you a savings account due to altruistic reasons); and the operational rewards the bank would use to run CI machines for GHC.

I hope this makes sense, and explains the concept of how this works in principle.