For starting a new article, you may first want to draft the article in a user sandbox named after the topic, such as
User:Stan Lee/Project X,
just as you would when expanding an existing article. Work on it until it meets the basics requirements for new articles: it should be based on significant coverage of the topic, in reliable sources that are independent of the topic.
When you are ready to make it live on Wikipedia, try asking an experienced editor you've encountered to look it over and see if it meets the basic requirements for new articles. If you can't find an experienced editor to check it over, go ahead and click the Move tab, then move it out of your sandbox to its final title.
In general, the sooner you move out of a sandbox, the better. Then, watch the Talk page for your article. You may receive more feedback on your edit once it "goes live" compared to when it is in your sandbox.
Your role as an Ambassador
Again, Wikipedia Ambassadors who are familiar with the Did You Know process should help students nominate articles that are eligible.