1st, try to get an ideal of where it's located from the
description of its location and from diagram of illustration....
Then you can try masturbating to it till you feel the orgasm... You
can do other things to yourself at the same time but avoid contact
with your clit and anal area... That should let you have a 'feel'
of how g-spot orgasm is like.... Note that you might not be very
comfortable with it or be able to climax so easily if this is your
1st 'g-spot encounter'.... In that case, you should give yourself
more time... Try to relax more... Do not overpush yourself... If
you can't do it the 1st time round, you can always try it again
some other time....
Also, if you're not too comfortable with the masturbation idea...
You can always try asking your partner to help you with a little
fingering if he's willing and gentle enough...? (I'm sure he'll be
most willing in most cases...? 
)
