It is recommended to use the direct Sia API integration as documented in the full renterd setup guide with S5. But S5 also supports the S3 endpoints.
First, you'll need a fully configured instance of renterd (the new Sia renter software) running somewhere. Here's a great guide which shows you how to set one up easily on the Sia testnet.
Next, you need to set up a S5 Node using the instructions available here
For configuring the S5 Node to use your Sia renter node, you will need to add this section to your config.toml:
[store.s3]
accessKey = "MY_ACCESS_KEY" # Replace this with the access key from your renterd.yml
bucket = "sfive" # Or just "default"
endpointUrl = "YOUR_S3_ENDPOINT_URL" # http://localhost:7070 if you followed the Sia renterd testnet guide
secretKey = "MY_SECRET_KEY" # Replace this with the secret key from your renterd.ymlAnd then restart the node with docker container restart s5-node
You might also want to enable the accounts system on your node if it's available on the internet or if you want to use it with Vup, see config instructions for details.