Some can be used at planting. Others need to be mixed and sprayed on. Choose what is right for your needs. No, I'm not talking about male pattern baldness. I'm referring to your grass.
Some lucky folks have naturally beautiful lawns.
All they have to do is mow it. For the rest of us, there is help. When looking for grass seed, know the different types. And full sunny areas. Then you need to know whether you want rye grass or Kentucky bluegrass.