Welcome to the forums!
OmniPlan's help menu material has a tutorial that walks you through the basics - click the "Quick Tutorial" link on the front page of the help material. If you email our
support ninjas, they're also happy to answer any questions you may have.
There are also a number of decent articles available on
www.ganttchart.org that might help. (
Here's one, for example.) Hope this helps!