The vanilla WoW Horde leveling guide you see on this site was originally made back in 2006 by Joana (AKA Mancow, or FuriousPaul).  The guides have been tweaked many times over the years to make things "faster".  The leveling guides were made because of all the messages I got from people asking me how I was able to level up so quickly on new realms.  I was first to level 60 on 7 different realms (3 with Mancow and 4 with Joana), even winning Blizzard's "First to Level 50" contest they held back in 2006.
Our initial runs exposed a few (expected) issues: the game sometimes crashed, didn’t recognize our modern video cards, and was incompatible with our current login system. That first pass also couldn’t support any of our modern security and anti-cheating capabilities. Clearly we had a lot of work to do to make WoW Classic live up to the Blizzard standard of quality, and deliver the experience players want.
 ":"  -  Any time a step ends in a ":" instead of a "." means that the next step is part of the current step you are on.  This generally means the next step should be done while working on the current step.  This means every "start working on" or "continue working on" will end in a ":".  But this is used with other occasions as well, so keep this in mind.