"Wait, did I miss something?!"
No, we're working a little backwords.
As an introduction to smart contract security your assigned reading is... a bunch of audit reports.
Some firms have generously made such reports available. (THANK YOU)
This accomplishes a number of things. As presumably someone already in security, you can imagine.
First, such reports typically convey findings with enough explanation for non-security people while also giving all pertinent details.
Second, you get an idea for how you want your reports to be in the future. What do you like? Dislike? Having your report style in mind as you test just helps things go smoothly later.
Without further ado - get reading.