how do i start a new lawn theres nothing there but dirt

tickle

If if its good dirt, that is to say if its dusty then it isnt good. Get a load of top soil delivered, by the yard, and level it out, rake it and sow some grass seed. Buy grass seed according to your landscaping conditions, i.e. sunny/shady. Grass seed can be bought for shade, etc. Or you can have it sodded which is quicker more productive but expensive.