How to use my own type

I am trying to make a list of my own type , however, unity doesn’t seem to recognize that the type exists (even though I have the cs file of the type in the assets)
How would I go about having unity acknowledge my type?

I assume you already know how to make a list.

There may be a few reasons:
1-Are you sure you have saved your script? If there is an asteriks after your script name it is not saved.
2-Does the script and class name match?
3-Do your sciprt have any syntax and complier errors?
4-Is your class public? (Both your type and the class you make list on)
5- Does Intelli sense suggest your type as auto complete?

Also please let me to see your code and the error.