Before you can install your first custom skin, there are a few directories that you must create. This is a one-time step, and after completion you will simply copy files into these directories to install new skins. To create a directory in Windows, Right-Click in the folder area, select New -> Folder.

First off, locate your "Steam" directory. For most of you, it's probably at:
C:\Program Files\Steam\

Next, browse to your "cstrike" directory.
Steam\SteamApps\(your@email)\counter-strike\cstrike\

Several directories we're going to need aren't there yet. Let's create them:

Steam\SteamApps\(your@email)\counter-strike\cstrike\models\
This is where most of the custom model files will go, with only the exceptions below.




Steam\SteamApps\(your@email)\counter-strike\cstrike\models\shield\
Any model with "_shield" in the name should be placed in this directory.

C:\Program Files\Steam\SteamApps\your@email\counter-strike\cstrike\models\player\
This is for player replacements. Each player gets its own directory, so the following 9 folders will need to be created under the "player\" directory:
arctic, gign, gsg9, guerilla, leet, sas, terror, urban, vip
(...obviously with no commas in the names.)



Those are the main directories needed. You can skip ones of those that you won't be needing (ie, if not installing any player replacements, you can skip creating those directories).
In addition to the custom models themselves, there are sometimes extras included in the packs, such as sounds and sprites. Determine which of the following folders you will need, and create them as well.

For custom sounds, let's look at the required directories:
Steam\SteamApps\(your@email)\counter-strike\cstrike\sound\

Under that new directory, we'll have several directories to create:

Steam\SteamApps\(your@email)\counter-strike\cstrike\sound\player\
Holds the sounds that players make when moving or taking damage.

Steam\SteamApps\(your@email)\counter-strike\cstrike\sound\radio\
All radio calls and hostage replies.

Steam\SteamApps\(your@email)\counter-strike\cstrike\sound\weapons\
This is the directory we'll be most concerned with. Holds all the sounds that any weapon in the game makes, including knives, guns, grenades, and the C4 explosive.

Finally, custom sprites.
Steam\SteamApps\(your@email)\counter-strike\cstrike\sprites\
Pretty much all of the custom sprites go into that one big directory.

Whenever you install a custom model, make sure you copy each file into the appropriate directory, or it will not function properly.

tutorial by "csnation.net"