On twitter what do all the different things mean e.g #?

[Jack]

So I'm new to twitter and I haven't tweeted yet because I don't know what @ and # mean, when do you use them how do you use them any asnwers welcome thanks!

[Lowenna]

@ Is a username for a person if you search up '@username' you'll find then and if you mention them in a tweet you use their @username. # Is a trend it promotes tweets to the hashtag it was assigned to. say i tweeted '#Life' then if you search 'life' in the search bar you'll see my tweet and everyone else who has tweeted that.