Having an ad blocker on may be preventing you from seeing this option. Ad blockers tend to cause troubles not only in our Ads Manager but also in those of other ad platforms as well. For some advertisers, ad blockers may result in an "Error" or a "Your ad has 11 errors" message in the Ads Manager.
Please turn off your ad-blocker and refresh your page. If you have browser extensions, check to make sure they do not have built in ad-blockers. You should see an option to create a campaign on the upper right corner on the Manage Ads tab.
If you continue to run into issues, please contact us and include screenshots of any messages that appear on your screen.