I don't know of anyone that does OmniPlan training on a formal basis, but if you haven't done so already, chapter 3 of the manual might help some. You can get the manual
from this link.
Additionally, we can do our best to answer your questions here on the forums, or if you send an email to
omniplan@omnigroup.com the Support Ninjas are happy to answer questions, as well. If you send email to the ninjas, you're guaranteed a response, actually.
(The 'Send Feedback...' link from OmniPlan's help menu also sends email to that address, with a bit more information which helps us out - like what version of OP you have installed.