If the existing base, aka the ground that’s there, has 2-3 inches of soil, you can go right ahead and compact it. A hand tamper will suffice. If it’s too rocky, you will want to ship in some fill soil.
What is fill soil? Fill soil is basically dirt that one would expect to dig out of a hill or a hole for a basement or swimming pool. It’s just regular dirt that’s been there for millenia.
Once that’s compacted, you want to add another 1-1.5 inches of top soil. Top soil will often but not always look black. It’s the stuff that you want your grass roots to dig into. It is very important that you do not compact this layer. You want to spread it out and then gentle rake it with a hard rake, also known as a landscaper rake. Be sure to do this in a way to avoid stepping or rolling over previously raked areas. You want it nice and fluffy. Also note that while many landscapers will suggest 4-6 inches, that is far too much and is only necessary if there was no soil at all in place. Also keep in mind that sod comes with a layer of soil as well.
Once the base is prepared, have the sod delivered. Depending on conditions, sod should be used within 3 days of its harvest. If it’s left out in the hot summer sun, you will want to use it right away or keep it moist.
When installing sod, do so in a way to avoid stepping on areas that were just laid down. Sod pieces need to be staggered like a brick wall pattern. Ensure sides are pinched together. There should be no bumps or air pockets. Sod should have full contact with the top soil.
IMPORTANT: If there is existing vegetation whether it’s the old lawn or weeds, it’s important that they are removed. Putting new sod on top of vegetation will create bumps and will cause parts of the sod to die since the roots are unable to make contact with the top soil.
It will be necessary to cut sod whether it’s during the interweaving process or in round corners. Avoid using box cutters as they will dull and be useless within a few minutes. There are specialized tools that are serrated curved blades specifically for cutting sod.
If you are installing the sod in shaded areas, it is important to overseed with shaded blends on top of the sod. The reason is that sod varieties are always for full sun. Putting sod in shaded areas will cause them to die over time. The idea is the seeds will take over as parts of the sod die.
Finally, it is important to keep the roots moist over the first 3-4 weeks. To do this, simply peel back a corner like one would a carpet and feel the underside. You want it moist not flooding nor dry. Once the blades are about 4 inches, you may cut the grass.