How do I add gr to my garden?

You would need to remove the pebbles first. You should save the pebbles for another landscaping project. My suggestion would be to lay sod. You would have an "instant" lawn. Planting gr with seeds is an iffy process. You could have patches that do not come up. If your soil under the pebbles is good then you could just lay the sod on top of it. Before laying any sod or planting seeds you should get a soil sample first. You could waste alot of money by not getting the soil sample because you might choose a gr that will not grow in your soil. Contact your county agent or go to a QUALIFIED plant nursery (not a home depot or lowers) for information on obtaining a soil sample and planting process.