We can all read the page on Twitter about the Twitter hashtags so I'm not going to regurgitate all that but just give you practical examples of how you can use them to your advantage.
The original idea of the hashtag was to make it ewasier for your tweet to be found by anyone doing a twitter search for a given subject. For example if I were tweeting about a new networking group I might write:
“Are you attending the Toledo BOB club #networking meeting this morning?”
Anyone interested in networking might well do a search to find other like minded people and assuming that they are searching close to the timeline of my tweet then they're likely to pick me up and follow me.
TV programs are picking up on the use of the hashtag which allows people to follow and comment on a current event of debate. The one that immediately comes to my mind is #bbcqt which is for a political debate held every Thursday evening in the UK at 22.35 GMT
In addition, hash-tagging a word is more likely to turn something into a trending topic but don't get carried away thinking that typing #networking is going to go viral all of a sudden.
It's as simple as that.
Having said that, Twitter hashtags have taken on a guise as a punctuation mark or indicator of something said either in humour, sarcasm or what you might say under one's breath. To give you an example:
“I love getting up early for networking meetings #likeIneedaholeinthehead”
Or an expletive that you might blurt out whilst coughing:
I like Todd, he's a great guy........#idiot!
OK for it to be really funny you maybe need a slightly stronger hashtag but for the purpose of this discussion I hope that you get the point.