Work through the "Get started" section of the official docs[1]. After this you could take a look at Awesome Flutter[2].
If you are more into video tutorials, this one[3] is pretty compact but not made for total beginners.
If you really want to get into it, you could now start checking out a not too big Open Source project like Musify (music player)[4], Localsend (file sharing)[5] or immich (photo sync)[6].