Do we have some standard tutorials in the YouTube about OKD for biginners
Welcome to the ODK forum, @Atta! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
@yanokwa has posted recordings of webinars that give an overview of ODK and give details on some of Central's features.
I think "Humanitarian Data Solutions" has some good tutorials:
You can also just search "ODK" on YouTube and all sorts of videos come up.