Help needed regarding security in PeerPad

Hi, Would like to know more about how security works in PeerPad.

There’s a great document explaining the security model in the project’s repository:

Could you please tell me How keys are generated when I click Start/Go in browser.?
Also how it generates Read key and write key?

PeerPad uses the local store to store some records. - does that mean it uses browser cache?

In order for this to be safe from people with access to the local store that don’t have the key, these records are encrypted using a symmetric key derived from the “read key”.
I did not understood this part also