Hair Brushes are used in a graphic program.  They are like "stamps"  that when applied create a shape of some kind. In the case of hair brushes, the stamp results in an image that resembles hair strands or clumps.

You can buy brushes or you can find them free.

There are loads of free ones at DeviantART.

Free Hair Brushes

I don't know what graphic program you use, but there are brushes for Photoshop and also for Paintshop Pro.  You can also use Photoshop Brushes in Paintshop Pro

You can look for Paint Shop Pro ones or convert Photoshop ones so that you can use them in Paint Shop Pro.

http://abrviewer.sourceforge.net/

It's really easy to use.

 

1.  Install it;

2.  Put your unzipped Photoshop brushes in a folder;

3.  Click ABR Viewer icon;

4.  Click "select folder" button and browse to the folder that has your Photoshop brushes in it;

5.  Double click each brush name that appears in the top left window. This will scan the brush file and produce images in the left side;

6.  Click "Export" and then "Thumbnails".  That saves the images you see as .png files;

7.  To clear the image preview window,  select the brush names in the left bottom window using "CTRL + left mouse button", then right click and "Close All".

 

Repeat the steps for each Photoshop brush you want to convert.

Once you have your .png files... open PSP and use batch conversion found in "File" and "Batch Conversion" to convert the .png files to .psp or .pspimage files.

You can leave them like that and use them as copy/paste type "tubes", or you can go through the process of installing them into your "tubes tool" or make them into brushes. Unfortunately you have to recreate the brush one file at a time, which is quite tedious.

Here is a tutorial that gives you an idea of how to use hair brushes to make hair:

http://www.antjesgraphics.com/AGTut.html

If you want to just use digital painting, here is another tutorial on how to paint hair:

http://features.cgsociety.org/story_custom.php?story_id=3174

There are others too.... check this thread:

http://market.renderosity.com/mod/forumpro/showthread.php?thread_id=2660658
 

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi