Google Tweetdeck, and download it - takes seconds - and then register your account.
Re the hashtags, often people use them to add a bit of humour to their own posts, in the same way that you might see on here - an example:
Breakfast this morning was toast and coffee. #cantfacefoodinthemorning
I know that's a silly example but couldn't think of anything more creative!
On here, someone might post along the lines of:
Busy day today, and I'm really knackered.
A 'real' hashtag is used so that you can search/join in on a trending topic.
So if, let's say, there was a big conversation going on about Mumsnet, someone will start a hashtag #MN - you can search the hashtag and create a whole column (on Tweetdeck) to see all posts that have been made using that hashtag - which makes it easier to join in.
You get people to follow you by posting! People will see what you've posted and will choose to follow you - but also, your posts may get re-tweeted by a follower, which means that their followers will see your tweet - so people who aren't your followers get a chance to follow you.
The more you post, the more you will get 'seen', and therefore are more likely to be followed.
I have two accounts on there - one in my real name, which I use very rarely. I must be on some kind of list somewhere, as despite very, very infrequent posting, I regularly gain new followers - I have well over 300 now!
However, one thing that does happen is that companies use 'bots' - programmes that search the internet for key words - so if you post about dieting, let's say, you will suddenly gain various diet companies as followers. I regularly go through my list of followers and cull those who I deem to be bots or likely spammers.
As Mme says, you can't lurk on Twitter - jump in!