Scott Kelby has updated his classic: How Do I Do That in Lightroom, 3rd Edition to include the new masking tools.
If not familiar, Kelby takes Lightroom workflow tools and tells you how to do a tool in one page, step by step. Great quick reference when one needs to know how to do something without looking up on the computer.
Purchased my copy at B/N Asheville (like to visit bookstores) or online at B/N and Amazon:
Amazon link: https://www.amazon.com/How-Do-That-Lightroom-Quickest/dp/1681989158/ref=sr_1_4?crid=1YV5SXRMPVDWM&keywords=scott+kelby&qid=1669040874&sprefix=scott+kelby%2Caps%2C96&sr=8-4