I haven't tried any of the tears with brushes-looks easier but here is a general for how I do mine.
1. Use freehand lasso tool to select area you want to delete - feather by 2 pixels and then delete.
2.Use the freehand lasso tool on the remaining area to make the tear part- use an irregular path -some wide areas and narrow areas as tears aren't always even -feather selection by 2 pixels then Ctrl+J to paste to new layer.
3. Ctrl+U to adjust hue and saturation - lower the saturation and increase the lightness until it becomes white.
4. Filter>Noise>Add Noise>GaussianBlur - check the box with monochromatic -play with slider for amount but a single digit number should be sufficient
5. Filter>Filter Gallery>Texture>Craquelure and play with the settings -you don't want any thing real harsh
6. Filter>Blur>Motion Blur - set the angle in the direction ofthe tear and just use a slight blur setting 2-5
***If you would like to save this tear for future use select it and copy and then paste in new document (file from clipboard choice) and save as a PNG file
7. Nudge the tear layer out away from the paper edge a bit then merge the tear and paper layers. Apply drop shadow
If you want to get really technical and picky you can use the smudge tool at a very small setting to pull out "fibers" a bit from the patterned paper into the tear area. I also do this on the torn white area to pull out fibers. Kind of tedious but more realistic if you will be printing out the LO.
Again- there are so many different methods and mine is a combination of techniques I learned from different tutorials. Digital Scrapbook Place had some tutorials on paper tearing when I fist got started. Would be interesting to see one using the brush technique as I haven't seen that and it sure sounds interesting. Hope this is enough to get you started.