Everyone
starts from the beginning
... in the beginning ... so don't feel alone :)
I am sure you know more than you think you know about Object Oriented Programming because: OOP models, in software, processes of categorization by relatedness, and hierarchic order, patterns of inference, deduction, syllogistic reasoning, etc., that go on in your brain every day ... cognitive processes, without which, you could
not function in daily life to drive a car, or order a meal.
I suggest you focus on getting a good book on OOP to study. Diagramming, outlining, they all help; "design patterns" are an interesting way to abstract out common tasks encountered in programming frequently.
For OOP in C#, you might consider Dan Clark's book, for example: "Beginning C# Object-Oriented Programming:" [
^] (2013, APress).
For Design Patterns, there is a commercial library of C# implementations called the ".NET Design Pattern FrameWork," available from DoFactory: [
^]. I found some good free material on Design Patterns at their web-site before I became a customer: I did end up purchasing the library.
The one book I bought on Design Patterns, "C# Design Patterns: A Tutorial" by James Cooper (2002, Addison Wesley) [
^] is one of the worst technical books I've ever seen, and I suggest you avoid it.
I have a friend who likes the "Head First" series book on Design Patterns from O'Reilly (2004: [
^].
I find the Head First series books stuffed full of graphic illustrations that are "cute," but have no real educational value. But, perhaps, I am not a "visual thinker."