You're welcome!
"Are Diads single notes?"
No, diads are 2 notes played at the same time. The term "diad" means "a pair of something". In this case 2 notes played together.
This is an A5 diad because the note A and the note E are played together and they are a 5th interval apart.
|----------|
|----------|
|----------|
|--2-(e)---|
|--0-(a)---|
|----------|
That's followed by an A6 diad. The note A and the note F# are played together and they are a 6th interval apart..
|----------|
|----------|
|----------|
|--4-(f#)--|
|--0-(a)---|
|----------|
I cover the picking & fretting of combining those as a bluesy riff in tutorial I linked above.
https://www.guitartricks.com/lesson/9968
"I was also told that there is an excellent fingerstyle course in the acoustic section of the website where do I find this?"
Depends on your skill level. Anders does some good beginner fingerpicking lessons in the GF 2 course.
https://www.guitartricks.com/lesson/31449
Lisa does some good fingerpicking tutorials as well.
https://www.guitartricks.com/tutorial/596/next-lesson
You can find a whole series of fingerpicking tutorials in Lisa's instructor directory. Scroll about halfway down the page.
https://www.guitartricks.com/instructors/311296
"Are there any lessons on flatpicking from beginner stage and onwards please."
I cover basic picking technique for picking single note lines in the form of scales in my old GF 2 course.
https://www.guitartricks.com/lesson/13232
https://www.guitartricks.com/lesson/13236
Best of success!