If you have ever renovated your lawn, you know how big of a chore it can be. If you are replacing it manually, you first have to remove the old grass, then prepare the seedbed, spread the seeds and keep them moist until they germinate. By using a slit seeder, you can make a few of those processes much easier---virtually no seedbed preparation and you don't have to spread the seeds by hand. The slit seeder doesn't need a prepared seedbed because it injects the seeds right into the ground. With a little practice, it is fairly easy to use a slit seeder.
Prepare your lawn for seeding. This may include a complete grass kill using a nonselective herbicide or scalping your lawn with a lawn mower if you are planning on over-seeding your lawn.
Fill the slit seeder with gas and fill the seed hopper with grass seed.
Set the slit seeder application rate to half of your intended total application, because you are going to do the seeding twice.
Run the slit seeder in parallel paths over the entire lawn. You will be driving it much like you would a lawn mower--the paths should be tight to each other.
Run the slit seeder over the entire lawn again, this time perpendicular (90 degrees) to the first path.
Fill your lawn roller with water and roll it over the entire yard. This will encourage seed-to-soil contact to help promote germination.