Healthy soil is a complex ecosystem containing roots, rotting organic matter, minerals, earthworms, bacteria and a myriad of other living organisms. An ideal home for your future herbs and vegetables ! You will want to keep your soil this way, and not put in herbicides or other chemical weed killers when you start a garden. Also (in my opinion) “tilling” the soil is unnecessary in many cases and simply disturbs the resident organisms of the soil, including the earthworms !
Find an area in your grass yard that receives good sunlight for several hours, that you want to convert to a garden plot. Cover the intended area with flattened cardboard boxes to stifle the grass.
In the meantime, start the vegetables or herbs that you would like to grow in small pots. Also gather some leaf mulch and compost.
After a week or so, move the cardboard boxes aside and pull out the yellowed grass by hand. Then transplant the seedlings you have. Spread a layer of manure and/or kitchen compost on the soil, then cover with leaf mulch. Don’t forget to water !
You can always add wood borders to your garden plot later on. What’s important is that you’ve started your garden !