I understand that one can follow people on twitter. But after searching keywords and results displayed where to locate option to follow the keywords or hashtags
Basically: just search for your hashtag. At least, that's the method if you're not using a service like Tweetdeck. It's also worth noting that you can "save searches" for quick access later.
We're using for our own company https://twitter.com/search to see what people are talking about when it related to us. So give it a try and it should help you follow keywords.
Besides Tweetdeck,you can also use other services mentioned in the link below -
I thought that tweetdeck was stopping it's service...
Nope, just the old-fashioned Adobe Air version. If your TweetDeck has a yellow icon it's time to upgrade, but those using the web version or the desktop version with a blue icon can keep on using it.
You can't follow a hashtag directly with your Twitter account, but third party software such as Tweetdeck will let you do that with a "hacky" solution. You can set up a column with Tweetdeck to search for a hashtag and it will update automatically. This is essentially the same as searching for a hashtag on Twitter, but on Twitter it will not automatically update for you. Plus, with Tweetdeck you can save the column so it's always there and updating when you turn it on.