As the old saying goes, instead of giving you a fish, I'm going to teach you how to use a fishing pole. Or however that went.
First off, make sure the map that you want to host is in your GHost++ maps folder.
Next, create a new text document, and copy-paste the code below, and replace (MAPNAMEHERE) with the name of the map. Not the name you want it to be called, but the actual name. For example, DotA Allstars v6.63b.w3x.
Save this text document as a .cfg file. Whatever you type as the filename, will be the name you need to use with !load. For example, if you named the file "island defence.cfg", then you would type "!load island defence". This is assuming your trigger is !, though.
Code
map_path = Maps\Download\(MAPNAMEHERE).w3x
# map speed
# 1 = slow # 2 = normal # 3 = fast
map_speed = 3
# map visibility
# 1 = hide terrain # 2 = explored # 3 = always visible # 4 = default
map_visibility = 4
# map observers
# 1 = none # 2 = on defeat # 3 = allowed # 4 = referees
map_observers = 1
# map flags
# - you can combine these flags by adding together all the options you want to use
# - for example to have teams together and fixed teams you would use "3"
# 1 = teams together # 2 = fixed teams # 4 = unit share # 8 = random hero # 16 = random races
map_flags = 3
# map game type
# 1 = custom # 9 = Blizzard # 2 = custom melee map
map_gametype = 1
# map local path (for map downloads)
# GHost++ doesn't require map files but if it has access to them it can send them to players
# GHost++ will search bot_mappath + map_localpath for the map file (bot_mappath is set in the main config file)
map_localpath = (MAPNAMEHERE).w3x
Hopefully now you know how to fish.