1.
For some Canon EOS cameras there is an extra switch under the lens mount in the body. This switch is at about 10 o'clock position when the camera is facing you. The function of this switch is an old way to allow the EOS camera body to judge if the lens mounted is a EF compatible lens and so it is a pre-requisite to switch it on if you want the electronic functions from the EOS camera.
Not all EOS camera has this extra power switch. It only exists on most Film EOS cameras, 1-series Digital EOS cameras and D30/D60. Newer consumer grade Digital EOS cameras like 10D/20D/30D and 300D/350D do not have this switch at all so you do not need to care about it when using these camera models.
　

2.
This EOS switch is a "spring-type" switch in that it rests on the lower position of the slot when no lens is mounted.

3.
The switch is free to move in it's slot as shown and the camera recognises there is a EF-compatible lens/adapter when this switch is pushed to the upward position.

4.
Since it is a "spring-type" switch you have to insert a small piece of paper or cardboard to hold it in the ENABLED position. Every EF compatible lens, either from Canon or third-party manufacturer has the provision to trigger this switch when they are mounted on the body. So by inserting this small piece of paper it is absolutely non-damaging way to doing the equivalent with our lens adapter and will not harm your warranty anyway.

5.
We recommend using soft material (such as small piece paper) for this purpose. Just make sure it fills the switch slot cavity and keep the EOS switch enabled. Now your EOS camera is ready for using our adapter.