You don't need to disable any keys. All conditions need to be true for an event to run, so you add conditions to your movement events to check if they can be run. Here are a few ways to do this, I've given two examples.
The first says if sprite is within 100 degrees of 0 (facing right) and right arrow is pressed, then move right. If the sprite is facing left (180 degrees), this event will not run.
The second is inverted, which you can access by right clicking a condition. The condition is that this event can run if the sprite angle is NOT facing 270 degrees (up).
To answer the question of how to find the angle specifically, you're going to use "Expressions". In this case, Sprite.Angle will give you the angle of the sprite. Here is more about expressions - https://www.scirra.com/manual/78/expressions
Regarding why people give advice logic first instead of straight code, there are many reasons.
One is that there are usually many ways to go about achieving something, and without seeing what you have done or what approach you have tried, a certain method/example provided may or may not work for you. This is why it is recommended to post your own capx when asking for help - tips-for-posting-in-the-quot-how-do-i-quot-forum_t62843
People generally want you to figure it out on your own first so that you can really learn it instead of just copy pasting code. We hope that a logical hint can get you moving in the right direction, as many problems stem from a logical misunderstanding - like when you were trying to disable keys (which is a possible solution by the way, just more complicated).
Also we literally can't just copy and past code from Construct, we need to make it, take a screenshot or save a capx and then upload it. I myself don't always work on a device with Construct on it, so I can give logical advice but not provide an example right away. Another reason to provide your capx, so we people don't have to recreate your problem from scratch.
Another reason may be because your questions were too general. Again, there can be many solutions to a given problem. If you ask a general question, you'll get general advice. This usually leads to more specific questions which will get answered. Again, yet another reason to post your capx or what you have worked on yourself first.
EDIT: tl;dr version: You have the highest likelihood of someone responding with a specific capx example if you provide your own capx first.
From your first post, you asked how to fix the space between body parts. What space between body parts? We have no way of knowing what your snake looks like, or why there is space to begin with.