There are some how-tos at the
HLO Wiki, though I have to admit that I've learned mostly through trying stuff.
For resource searching and lookups I've been relying on the
Archives of Nethys and the
Pathfinder 2 easy Library.
There are things I like about HLO; the die roller is generally superior to HLCs, and with the Gamemastery Guide tools it's got a nice interface to build custom monsters and complex hazards.