It does start off difficult. It took me a week to make a monster constantly move up and down.
My advice would be to have a good understanding of how the graphics window work: how the coordinates are laid out like and how these coordinate behave: do they stay the same, increase or decrease? Like how the origin is on the top left of the window, x increase as you go right but y is constant. y increase as you go down but x is constant.
At the end of the day, they are just a bunch of logic more specifically if and else statements. A bunch of if and else statements.
Then take these ideas and write the ideas and the logic down a piece of paper. Just debug the code on paper and figure out the problems in the code. The bug can only be in one place and it will never move. Sometimes, it can also be logic that you forgot to write. I experience this when I wrote my first basic AI code.
The reason why programming books don't teach you these things is because programming is a general idea. There are infinite posssibilities on what you can do with it. You are not suppose to "plug and chug" and guess it is going to work. It needs to make sense and that can only be achieved through understanding, logic and being methodical the same why you would approach a math or physics problem with that kind of mindset.
It is like saying "why don't books teach you how to make final fantasy or starcraft or zelda? At the end of the day, the games share basic code structure. Besides, it will spoil the fun and also prevent the reader from experimenting and doing it themselves. You are suppose to have an open mind and use that mind to come up with the code yourself. That is the beauty of programming. It is suppose make you tap the power of your mind.
On top of my head, try getting the snake head to move. If you can make it move in all for four directions, try making the body movement along with the head. Take it one step at a time and build off of that.
There are many ways to solve it. This is just one way I came up with on top of my head.
Good luck.