first, look up how to tie a munters (sp) hitch. That will help a lot.
It might be a little difficult with 3 beaners, I usually use 5. Your ling will just be twisted instead of flat.
1. Set up one anchor.
2. Munter hitch a beaner to one end of the line. Wrap it around the tree and clip the line to itself. (this is your 2nd anchor). Make sure to fold the webbing in half when clipping it on, so the webbing doesn't end up turned on it's edge.
3. Clip your 2nd beaner to the first anchor.
4. Keeping the line flat, munter hitch a beaner to the line about 5 feet away from your first anchor. (Distance varies based on line length.
5. Take the tail of your line, run it from the bottom up through the beaner on the first anchor.
6. Don't let the tail twist.
7. Run the tail from the 1st anchor to the beaner 5 ft away, clipping it in from the top down.
8. Run the tail bottom up through the beaner on the first anchor. At this point, pull the tail UNDERNEATH the webbing already on the beaner. This will help the system lock via tension.
9. Run the tail top to bottom on the beaner 5ft away in the line. Do the same thing as before, pulling it under the previous wrap.
10. At this point, pull hard towards the tree, the line should tighten and lock.
11. If you don't understand this, google it. or youtube it.