How does tweeter work?

[Saires]

I have no intention of gettin a tweeter account however everyone keeps referring to it, radios, tv's etc. so help me to understand two things I keep hearing regarding tweeter.

First one " Hashtag something"- what does hash tag do? Or what does it mean when placed in front of a word, what's its function?

Second one "@ someone"- does this mean your tagging someone like in Facebook or is it something else altogether?

I do use Facebook and I've started using instagram (only so I can get inspired by others pictures of around the world). I'm just not a fan of "following" what someone has to say, but since it's becoming an everyday thing then I should get on this band wagon