Can someone explain to me # and @?

[the DT]

In relation to Twitter, that is. I am new to it and don't understand if, when, and how to use these symbols. Please explain it as if I had little or no knowledge of technology (true) and make no assumptions on my abilities to understand any technological terms, phrases, or words. Thanks for your help.
Yes I know that it means 'number' and 'at' but what purpose does it serve to use these with Twitter. What happens when I use one of these symbols, in other words, is there an ACTION associated with them?

[Jacob]

means number, @ meants at

[Monkey]

I'm not a huge twitterer but the @ means that you are directing your tweet at some person. So it would be @sometwittername and then the rest of your tweet. Its known as a direct message.

The #, I may be wrong here, but I believe it's that you discovered something. So it's like you say something and then #peopledon'tusefacebookanymore. I've never seen one with a space separating the words before.

[Seah Han Wen]

@ is when you are directing a twitter post to a certain someone.
Usage : @someonetwitternamehere What's up?

# is known as a hashtag in twitter. Basically, it is like a tag that you use for your tweet.
Example, if you use #bananas
someone using the search bar and searching bananas will see your tweet listed,