Magpie hit it :P
The 'Tao' is something that cannot be explained and if you did you will be told it is incorrect, but it is simply 'everything'
anyways the point of becoming nothingness is this. we have desires and are not happy until we have achieved or reached our goals or desires. by letting go of desires until we have nothing we have everything that we want and therefore are happy with everything.
nothingness could be seen in its opposite as 'everything'ESSa described in the yin yang symbol, they are both equal to each other and both run into each other.
Taoism doesn't specifically teach us anything other than to exist in happiness without the need or desires for anything so our mind is at peace.
just to clear this up, in the beginning Taoism was in no way a religion, it has no rituals, worship, Gods ect and was purely a philosophical way of life. at some point Taoism had a sort of 'branch off' if you like and created a more mystical almost magical religion which worshipped God's, heaven and Earth ect. but most choose to follow the philosophical Taoism as it was in no way supposed to be a religion in the first place.
hope ive helped

x
EDIT: not trying to convert you or anything but the book 'Tao Te Ching' was written by Lao Tzu and is an awesome read for every day life whatever religion you are if any