First and foremost, you will need to have photoshop and also download the Pattern/UV sheet of the gun you want to create. We will be making a skin for the P90 since its one of the easiest. You can download the Pattern sheets here:  https://drive.google.com/folderview?id=0B6BFjXblqNzoLWRFR25BMk9oQXc&usp=drive_web#grid

You also need VTFEdit

At the above site, click SMG –> P90 , open and download the smg_p90.tga file.

Open photoshop, and open the .tga in photoshop. Resize the file to 1024 x 1024.

Duplicate the layer. Right click on the selected layer (Background) and Duplicate Layer, click OK.

Now you’re going to need a pattern. We will be using a random pattern downloaded from google images as an example. Open the pattern in photoshop, Go to Select –> All. Your image will be selected. Then go to Edit –> Copy.

Go to your smg_p90.tga file and select Edit –> Paste. Select the Magic wand tool. If you dont see it try clicking Shift+W. Look at your layers,on your right. Make sure you have your tga layer selected the background copy  (not the pattern). With your Magic Wand selected, click on the largest image of the P90.

Select the zebra pattern layer. Go to Select –> Inverse

Select the Eraser tool. Default (press E). Erase your pattern layer.

Save your finished file as a .tga.

Open your .tga file into VTFedit. Open VTFedit, click File –> Import and import your .tga file. Press OK to save as a .VTF file.

We are now done with the pattern creation. The next step is to open it up in-game. You need to have the developers console enabled first. To enable developers console, Launch the game (CS:GO), Go to OPTIONS –> GAME SETTINGS and Enable Developers Console (~) –> Yes. Press this (~) and it will bring up the developers console. This can also be used for hacking, but that’s illegal of course.

Type workshop_workbench into the console. It will open up this;

Click the drop-down, select Custom Paint Job. Select choose pattern and open your .vtf file. There are a few things you need to change as well.

You will need to change your gun to a P90 and drag all the offsets and rotation to the left. You can adjust the Wear dial to change the guns usage appearance. And lastly , make sure ignore_weapon _size_scale is ticked.

It will look something like this;

Its done, finally. In order to submit you will have to take some pictures and stuff. Just make sure the design is original. Use F12 to take pictures in-game. Vote for my design here: http://steamcommunity.com/sharedfiles/filedetails/?id=215798361  if you like it . Hope this was helpful.