i have a S2 IS canon and i want to take photos of animals and birds usually at long distances and also mountains can you please help me in selecting

You can't get a zoom lens for it, unfortunately. This camera's lens is fixed onto the camera, so the best you can do is get a teleconverter to double your lens range. A 2x teleconverter will magnify the images coming into your lens by 2. The downside is, that this will cause your camera to have to be compensated in it's exposure settings because of the loss of light by 1-2 stops. And depending on the quality of the glass in your teleconverter, you may also run into clarity issues. You will certainly run into some "barrelling" issues at the extreme end of your focal length. this will make the image look like you're looking out of a barrell. This can also happen with wide angle converters ass well.

To be honest, while you can purchase these options to screw onto your existing lens, I don't recommend them because the tradeoffs involved simply outweigh the benefits in my mind.