Collect a sample of the grass currently growing in your yard and go on the Internet and find out what type grass you have. If you decide to plant seed, buy good quality because the cheap stuff is loaded with weed seed. You also need to sow the seed generously and evenly. You can buy a hand sower that is economical and made of plastic so it is light weight. You will need to reseed the area once or twice more after the first grass starts growing. 2ndly, you can buy rolled grass sod. It does have to be soaked with water on a daily basis until it takes root (about 2 weeks). It needs less attention than the grass seed. The main thing is to plant the same type of grass as you already have growing in your yard.
"I have not failed. I've just found 10,000 ways that won't work." --- Thomas Edison