If you want to add a tube to your tubes tool in psp,
you need to open psp, click on File> Browse 

When you locate your tube, double click the picture to open it..

 Then click on File> export> Picture Tube..

This box will open, name your tube, and click ok

Your tube is now ready to use with your tube tool

I hope you enjoyed this tutorial,
 and I should warn you...collecting tubes is very addictive :)