That's an excellent book, let me add two more modern sauce books that might be a bit easier to understand and use, esp. for a beginner:
https://smile.amazon.com/Sauces-Classical-Contemporary-Making-Fourth/dp/0544819829 (my all-time favorite)
https://smile.amazon.com/Modern-Sauces-More-Recipes-Every/dp/0811878384
James Peterson's Sauces and Splendid Soups are a good place to start.
“Sauces” is a good one if you really want to dive in.
“Just Add Sauce” by America’s Test Kitchen is a good, cheap alternative for general info. You can buy it used much cheaper.
“The Flavor Bible” is a good compliment to either if you want to get creative.
#1 thing is to use the amount of salt on foods that make them taste good. It is extremely common for home cooks to use way less than this amount of salt. If you can taste the salt, you've over-salted (or it's sitting on the surface of the food), but the rule in good restaurants is: Use just less than that amount of salt.
More generally, I like to analyze the restaurant foods I like to learn what makes them work for me. Even if it's fast food (example: Popeye's does a terrific job with fried chicken). Then I can try to incorporate those skills into my cooking
I also see home cooks frequently use way too little sauce or none at all. This is a very general trend--in other words, there are a lot of foods that need a sauce of some kind! Example: A turkey sandwich without any mayonnaise at all is just . . . really dry, you know? Also salads! I'm not saying your salad greens should be swimming (unless you like that), but under-dressed salads are just . . . too much lettuce, sitting in a bowl. Sadly even in a lot of good restaurants I've been to, the salads are under-dressed :(
James Peterson has a terrific book on sauces that I highly recommend: https://www.amazon.com/Sauces-Classical-Contemporary-Making-Fourth/dp/0544819829
One of my go-to sauces for sandwiches and basically anything else is sriracha mayonnaise, which you can buy in the supermarket to save the time spent making the exact same thing (mayonnaise + sriracha). Also have you tried Yum Yum sauce? It's great and everyone loves it. Try dunking grilled meats in it the next time you grill
These are kind of some random suggestions that I think will help. There are now so many good recipe sources (but still a lot of not-great ones, esp. with simple Google searches, for some reason). I highly recommend the ChefSteps website subscription, they're great