Step 1: Visit https://feeder.finance/ and launch the app (graphic A).
Step 2: Then open the "Staking" tab and press the "Approve"-button. Approve the transaction and wait a few seconds until it is confirmed by the network (graphic B). The "Approve"-button goes away after successful approval.
Step 3: Now press the "Stake"-button (graphic C), enter how much you would like to stake (graphic D), and then press "Deposit". Approve the transaction and wait a few seconds until your transaction has been confirmed.
Step 4: After the successful confirmation of your transaction, you have successfully staked your FEED!
Useful resource: What is sFEED?