The order to look at the docs will be:
Requirements : https://peerplays.gitbook.io/community-project-docs/son/bitcoin-sons/son-requirements-specification
Functional specification : https://peerplays.gitbook.io/community-project-docs/son/bitcoin-sons/functional-pecs
LLDs : https://peerplays.gitbook.io/community-project-docs/son/bitcoin-sons/low-level-designs