Once you know the kind of information you want to search for on Twitter, merely use the search box and type in a word or term.
But for finding people or organizations of interest to you, it is helpful to know of specific hashtags. The following post with an infographic has a list of hastags and what each represents.
Let us know which hashtag groups you already use and which you might consider using in the future. Also. remember when you're tweeting to use hashtags to spread your tweet to a wider audience, increasing the likelihood of getting replies and carrying on a conversation.