URL generates gibberish value - i dont know why?

http://localhost:17059/evaluation/(S(ebixlhlqppu4prk5h4i3a2b0))/Login.aspx
i want it to generate only :http://localhost:17059/evaluation/Login.aspx
i dont know why this comes: (S(ebixlhlqppu4prk5h4i3a2b0))
how are URLs generated?

Thanks.