Hello Kapil,
First of all, you have to get registered with ICSI for foundation or executive level after completing 12th or graduation in any stream respectively. At the time of registration you get login ID and password. A student can apply for exam registration only after completing 9 months from the date of registration. First,you do student login / smash login at ICSI website and go to the examination tab and click on examination form. One page will get open having your all details and fill the module you want to give and click on proceed tab. After that they will demand payment ,fill all the details relating to online payment or whatever mode you have chosen. Take a print of your payment slip and you have done your CS examination registration.