You are given a string that you have to parse into tokens, which you can see in the "Token Grammar". For example:
str = 'return "String" + "number"'
From the table you must map each part of the string to a token from the table
result_tokens = 'return' - keyword; ' ' - whitespace; 'String' - string; ' - whitespace; 'number' - string
In addition, you need to implement an iteration protocol.
I hope this makes more sense to you.

I understand almost nothing from the description of this Kata and the examples given just can't make up for the 75% missing explanation. Can someone please explain me what I even have to do for this Kata?

HINT: You should probably try to make your function work the same, regardless of the spacing

Maybe try regular expressions, they are quite powerful but not that easy to get the actual pattern right

The spaces are quite easy to get around.

HINT: You should probably make your function space independent, as in working the same regardless of spacing

Most 4 kyu Katas I did were easier than even figuring out how to get started on solving this one...