Answer:
The way to tweets on twitter is by using what is called hashtags "#". By adding # + tagname you mark/tag the tweet. those who reply to your tweet will get the tag by default so that the conversation will be tagged as well. You can search twitter for these tags and then see all the tweets tagged with the same tag.
Many people tag their tweet when at a conference or event and that way people can see what people at the event are saying. There are services like hashtag.org that allow you to search by tags and also show you the trends/statistics of many used these tag over time.