I have been watching tons of youtube vids and I pretty much got the concept but would like to know if Im creating my designs correctly with strokes and fills.
"Correctly" depends a lot on the desired workflow and of course the output process.
If you have a question to a specific artwork, then please show it.
I . . . would like to know if Im creating my designs correctly with strokes and fills.
Well, without you demonstrating what you're doing and how you're doing it, we'd have no way of knowing whether you're making mistakes or doing it via "best practice". That said, it bears mentioning that there are always several ways to go about accomplishing a given end result in Illustrator. One method or another may be better for a particular output intent or deliverables plan, so context is important and always in play.
If you post an example (screenshot[s]s and detailed explanation), of something about which you're unsure, you'll get help here.
Regarding strokes and fills, as well as more complex versions of them (art & pattern brushes, free-form gradients, etc) it all depends on whether the finished artwork will stay at its original size and only be used in Adobe applications. If you are creating artwork that will be used in other non-Adobe creative applications and reproduced in a wide variety of methods then many of those effects will have to be "expanded" or "flattened."
For example, some of the graphics I create is sent to vinyl cutting plotters or computerized routing tables to cut shapes out of various materials (aluminum, acrylic, masonite, etc). In that environment the router bit or vinyl cutting knife blade will only cut where it sees a path present, basically the equivalent of what you see in Adobe Illustrator's outline view. A line stroke that isn't expanded won't be cut correctly. Art brush and pattern brush effects applied to paths won't even export properly to most other applications unless those effects are expanded into editable paths. I don't have to worry about those issues as much if the artwork is going to be output via a large format printer using an Adobe certifed RIP.
If the artwork is going to be re-sized at all yet stay within the Adobe environment care must be taken to make sure stroke and fill effects are scaled properly by applying the correct settings.