New to pool ownership - what is this part??

[mphsamy]

First post - hope I do this right!
Just bought a house with an in-ground vinyl liner pool. Been researching - found the manual for the Sand Dollar filter, but I do not understand what is this part attached in front of the strainer (which is in front of the pump motor). I think it has something to do with opening lines but nothing is marked. I am wondering if anyone knows what this is and what I do with it?
[attachment=1:2zcwulhf]what is this.jpg[/attachment:2zcwulhf]

 

[lbridges]

That's a 3-way valve and it controls which of the two pipes the pump draws water from. As pictured the pipe on the left is OFF and the pump would draw from whatever is connected to the pipe at the bottom on the pics. Turn the handle so that the OFF label points down and then the pump will draw water from the left pipe.