Extract to garrysmod/garrysmod/addons.
Sequel to Twitch Weaponry, a greatly improved now 20-weapon pack. With Twitch Weaponry, holding right-click allows you to aim the weapons more precisely, zooming in your view and allowing your crosshair to leave the centre of the screen. The new version adds stability fixes, 12 new weapons (including 5 faithful part-replicas of HL2 weapons), additional customisation options (that can be changed in their own options entry) and a 'slowmo' feature for singleplayer games.
This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons folder. You should end up with a directory structure similar to below:
twitch_weaponry_v2 <-- Addon folder!
- bullet-time (crosshair).txt
- bullet-time (no hud).txt
- tracer spraying mayhem.txt
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