Simple Java ArrayList stores and shows not repeated elements entered by user
Personally, I'd refrain from putting the bulk of your logic into the main method. I'd refactor the code out into other methods and just call them from the main method.

Also, I wouldn't consider 'while(true)' to be good programming practise with some exceptions. If I were you I'd get the ArrayList size and use a loop that runs up to that. This also removes the need for that if-break statement you have at the bottom of the while loop.

I would also note that the question outlined in the comments says to use an array, not an ArrayList which may or may not be important but given the student/interview style of the question it may need to be a normal array as specified...strictly speaking an ArrayList is an object that behaves 'like' and array.

In regards to comments although they are thorough I'd advise against writing comments on the same line as statements (unless they are very short) as it is inconvenient for anyone reviewing your code to have to scroll left and right just to read the comments.

Variable names could be a touch better too but this only really applies in a professional context where other people are going to be looking at your work (same as comments I suppose). Rather that use 'number' as variable name use something a bit more descriptive like 'usersNumber' or something like that...all goes towards easier understanding and readability. I should also note that this applies to method names too (eg. gimmeValue doesn't really make much sense).

However with all that being said, keep it up! Programming is all about refinement and practise and no doubt you'll be an excellent, clean coder in no time!