The readme.txt file contains many hints!

Installation –

Copy the “NOAMZ.bsp” file to:

“Cprogram files\Valve\Steam\SteamApps\ (your steam name) \half-life 2\hl2\maps”

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Playing-

Start Half Life 2 and open up the console (you might have to turn it on in the advanced controls options) and type-

“map NOAMZ”