Click on Start to begin an energy minimisation. You will be asked if you want to use an old or a new command file. You may be asked if the program should add lone pairs to the structure. If this question appears, click Yes. You will then be asked for a filename.
Any alphanumeric string is acceptable.
Capital letters are different from small letters. If files already exist with the name that you give, they will be overwritten. The minimisation should now proceed. If there are any errors in the message window, it may be because there are some hydrogens missing from the structure. Now try minimising again.