INSTALL IT
You have to put the io_scene_hl1map folder into a valid blender addon folder.
(replace "2.NN" with actual Blender version you use)
On MSWindows it cloud be : C:\Program Files\Blender Foundation\Blender\2.NN\scripts\addons
On GNU/Linux it could be : ~/.config/blender/2.NN/scripts/addons

ENABLE IT
Start Blender, go to File > User Preferences, tab Add-ons.
Filter on "Import-Export" category
Check "Export Half-Life 1 Tools Format (.map)" addon.
Press "Save User Settings" button if you want it to stay enabled accros Blender restarts.

USE IT
Use it by File > Export > Half-Life 1 Tools (.map)
Choose a path and file name with .map extension
Check options in "Export HL1 .map" side view.
Press "Export HL1 .map" button near the choosen filepath.