Thumbs up on chosing DOTA,for more information on DOTA and for stategies and help and all the stuff you need visit *www.dota-allstars.com
One more thing,you need loads of experience in dota,otherwise you will make an ass of yourself when you play against others,atleast 1 months experience is necessary.
and
*www.garena.com is a gaming platform which allows you to play lan games with many people around the world,just download it from there and for playing in rooms you need wersion 1.20 or higher.in indian rooms 1.20 is used.
you will need to have this software warcraft version switcher
*www.garena.com/forum/viewthread.php?tid=357119&highlight=warcraft+version+switcher
then set the path in garena and have fun!
any way if you need more help i am Blade-X in garena,or ask here.