Daniel is correct. May I suggest, though, before you apply, make sure you are registered for google adsense & earnings. Also, try to write at least 2-3 hubs a week for 6-8 weeks prior to your application. The team is looking for current high-demand participation. Also, if you have writing participation on other blog sites, that is helpful, as they request other online sources of your writing.
I had applied in hopes of being able to start in the fall when 4 of my 5 children are in school & I will have more time to commit to writing. I did not realize they were going apply my current level of hub production. When they sent their response, they told me to re-apply in 6 months, and to be sure I was writing at least 2-3 hubs a week to show them I can handle the high-demand of the apprenticeship - a minimum of 8 hubs a month. Also, they are looking for SEO written hubs -- so they told me. Some of my hubs were written specifically for SEO (more than 2/3 of my traffic is from Google), and some were not. They are looking for article-type of hubs -- no fiction or poetry. That's not to say you can't ever write fiction or poetry, just that the majority of your work should be SEO-content articles.
Hope I explained that ok, without too much gibberish!
Best wishes to you!