Congrats on deciding to major in ID, that's really exciting!! It's great that you are interested posting your sketches and improving. I totally understand where you're coming from about being nervous about posting your first sketches but don't worry, everyone has to start somewhere. Along this journey it's important to track your progress here, especially when things don't come out they way you want them to. Being able to scroll through your first posts see where you started really helps keep the motivation up when you're struggling on something down the road!
Since I'm still very much a learner in this area, I'm going to reserve all drawing comments to the pros of Core77.
You're doing all the right things by looking at youtube tutorials and and picking up a few books (great collection so far btw
). Having all of those books, I would say stick to 'How to Draw' to use as your core learning text, especially in the beginning. Scott Robertson has some great lessons on straight lines and ellipses that you should start with. Buy a stack of computer paper and work on your straight lines and ellipses following his exercises and just do as many sheets as you can every day. If you run out of exercises don't be afraid to make up your own and have fun with it! This will help to build up your muscle memory. Don't feel like you only need to do the basics though, sketching more advanced things like cars, shoes, and others will be fun and you'll learn things by just sketching them! Just make sure to dedicate a good amount of time to learning the basics.
The other two books are much less technical and give you more of a taste of the bigger picture of design sketching as a communication tool. They cover lots of topics and don't go into as much depth but they are really fun to read!
I'm really wishing you all the best and can't wait to see you progress! Have fun!