Twitter is introducing a new feature to timelines that will keep you up to date on particular ongoing events. At the top of your timeline, you'll start to see a Happening Now label that will show you all of the events and current topics Twitter thinks you're interested in, which when clicked, will take you to tweets people have posted about them.
Each event will have a little downward facing arrow in the top right corner. Tap that if you want to see why Twitter thinks you're interested in it or to hide it from your timeline. This new feature joins other recent Twitter additions including expanded tweet limits and an upcoming bookmarking function. As of now, Happening Now will only include sports events, but Twitter says the feature will be expanded in the coming months to include things like breaking news and entertainment developments.