Writing for online is both similar and different from writing for a print publication. When writing online you can include links to your sources or to other sites that further explain what you are discussing. You can include more pictures than you could with a newspaper article. Video and audio can also be utilized to bring more evidence to your article for your readers.
Writing for online journalism should be brief. No one really wants to scroll over and over again. The word count would have to be shorter and you may have to rely on more pictures to keep the audience from clicking away from your story.
Writing for print is also a bit more strict when it comes to word count. You only have so much space on a page and have to include other articles. I know for The Voice we have a 500-800 word count requirement to make sure we have both enough and not too much content.
Headlines are important no matter what media you are in. They draw the audience to the article and let them know what to expect to read about. Subheads can be useful in giving some more information if you opted for a snazzier/shorter headline