I would like to join a particular server in yor list, but when I click on "JOIN" It says what application do you want to open it. I,m not into computing really and I don´t understand what they want. I thought it would just open the server. can you help

Most of the join buttons require GT lite to be installed to assist with auto-joining the server. GT lite can be obtained from http://www.gametracker.com/downloads/