As a Fullscreen partner, all of your videos are monetized upon upload.
It's important to keep in mind though that due to the number of videos on YouTube's platform compared to the number of advertising agreements YouTube has in place, not all views will display ads. Online video monetization policies in certain countries can affect ads running as well.
YouTube also does not run ads on restricted content or videos with misleading or sensitive metadata (such as wording in the title, description, or tags that brands would not want affiliated with their product).
Videos with 3rd party claims also may not run ads, depending on the monetization policy that's set along with the claim.