One of the first things you need to know about operating HF (1.8 to 30 Mhz) is the current propagation conditions. There are a lot of complex solar weather reporting sites out there. Proppy, which is based on the VOCAP technology is an excellent and easy to use site.
On HF you’ll hear a lot of “Q Codes”. A great guide to understanding them is W5WWW’s page on QSL.NET
As a extra class, I can use the following bands:
If you’re curious which contests and events are on HF on any given day, check out this contest calendar from WA7BNM.