Its a section of urine.
Press 'A' to enter texture mode. Then open out a window in whichever view window you are in.
Example, if you have a texture for a car roof named roof.tga (256 x 256) make the TOP viewpoint active.
Press 'A'
Open out a window, it will be black and have Texture:NULL in the top of it.
Right click and select Load Texture.
Change the type (.paa, pac) to .tga and click on your texture.
The background will change to become your texture.
Press 'A' to leave texture mode.
Select the faces you require textured.
If they don't fall in the right place you will have to move the texture.
Press 'A' and use a combination of the following keys.
Cursor keys to move.
CNTL + Cursor Keys Move quickly
SHIFT + Cursor Keys - Resize window
Press 'A'
When you have your faces selected, with the texture in the right place behind them press 'B', its as simple as that.
So, Press 'A', right click, load texture, use cursors to manipulate texture, Select faces, Press 'B'
Good luck.
Note textures have to be a particular size (2 x 2, 4 x 4, 64 x 128, 128 x 128, 128 x 256) Powers of 2.
Brsseb's tutorials are really what you need, they are superb. Check out the sticky above this post.