How do I care for new or repaired grass?

Water daily...

Irrigate the soil daily, at least twice a day, but possibly more. Try not to let the soil completely dry out. When watering a new lawn, use just enough water to keep the soil moist at seed depth; standing water should be avoided.

Once grass emerges...

Once the seed has sprouted continue watering lightly, but allow the soil to dry slightly before watering again. At the seedling stage, it is even more critical not to repeatedly saturate the soil. 

Hurray, it's 2" tall...

When the grass is a couple inches tall cut back on water to once every two to three days, depending on the temperature. 

Time to cut,  4"

Once the grass reaches the cutting height for your particular grass type begin watering deeply, but less often, so the soil is wet to a depth of four inches. After watering, don't water again until the grass begins to show signs of stress. This trains the roots to grow deeper into the soil to reach available water and nutrients.

Your new grass...

Grasses are "monocots", meaning they emerge from the soil as a single blade. This single blade develops into a larger plant, but it will take time. Don't expect to have a thick lawn in a few weeks. It takes at least one full year, or more to get thick.