Not much to tell, so long story short. Go to the directory you want to ignore and select the way you want to ignore the files inside. Just read the following lines and you will get it.
- cd this/is/my/directory/with/files/i/want/to/ignore
- svn propedit svn:ignore .
After you have done this, you can edit the ignore file with your favorit command line editor (hopefully vi ;-) ).