Cal Newport defines deep work as the activities performed in distraction-free environments and argues that this is what's necessary to really make use of your full intellectual capacity.
The table of contents pretty much sums up the essence of Newport's line of argument: Deep work is valuable, but it's rare. And then he goes on to lay down some rules, some of which include quitting social media, structuring your day better and saying "no" to things than do not significantly help towards reaching your professional goals.
My favorite piece of advice was his suggestion on how to schedule your day: "Give every minute a job". Being an avid budgeter of money, I've always been looking for good advice on how to budget time. What he suggests is pretty simple, and won't surprise anyone, but I'll give it a go.
Overall, I think the book was good. He argued both with individual stories but also by citing relevant studies. I think Digital Minimalism was argued even clearer, but Deep Work was still a good read.