With SimpleID, you get full Blockstack access. This means your users can encrypt data client-side with keys that are entirely owned by them, store data in a high-performance storage hub (Gaia), and share that data privately or with the world.
Most of the Blockstack functionality is documented in Blockstack's docs, but there are one core piece you'll need from SimpeID first. Blockstack's functions are all contained within a class, similar to the SimpleID SDK. SimpleID takes care of initializing that class for you. The class variable that prefixes all Blockstack functions is
userSession and it is accessed from SimpleID like this:
const userSession = simple.getBlockstackSession()
Once you have that variable set, you're ready to use all of Blockstack's functionality documented here.