I don't program in C, but the first thing I want to say is that there are no integer arrays in KM. There are only strings, but KM allows you to fetch the Nth element of a string using and index that looks like a standard programming language index into a numeric array.
I'm a little confused by your screenshot. If you show the action where you are trying to use that string, I can probably correct you. But since I don't know the context, I'm not able to provide the solution.
You don't create a dictionary explicitly. When you assign a value to a key in dictionary, it's created. When you assign an empty string to a dictionary's key, that element vanishes forever.
Your question seems to indicate a slight misunderstanding. In your opening statement you said "a key called "Name", and a value called "Length"." but in fact the key in this question is "Joey" and its value is "11". There is indeed nothing actually called "Name" or "Length". So your terminology is slightly incorrect.
The most common way to do that is like this:
However most of the time you will want to specify the key as a variable, so you do it like this:
Notice how the variable, in this case MyKey, is inserted. It's an odd syntax, but you'll get used to it.
It took me several hours, or maybe days, to get used to dictionaries. But I'm glad they exist. They are pretty powerful.