Using Twitter is a bit like riding a bike, in that no one really teaches you how, but you just get on with it and learn what to do. With no official documentation, it can appear daunting; working out why some tweets have hashtags prefaced by #, some contain Twitter IDs prefaced by @, but others are prefaced by .@, and how web URLs end up in shorthand form, may seem some of life’s mysteries.
It also depends on which app (if any) you use to access Twitter. My own preference is Tweetbot, available from Apple’s App Stores for both OS X and iOS, which I find generally more helpful and reliable than Twitter’s own apps such as TweetDeck.
Once you are finding your feet, there are remarkably few guides to its conventions or more advanced features. Most users realise that each character can now include any Unicode characters, each of which costs you just one of the maximum of 140 characters in a tweet. But there is a lot more to Twitter: Eevee has written an excellent guide to some of the less well-known features here.
I have used Safari’s Export as PDF feature to save this as a permanent reference. Thank you, Eevee.