A sharp flat-edged spade can be used to slice out the sod. If you have poor soil and need to amend it with organic matter or other nutrients, removing the sod may be your best bet, so that you are able to till in the amendments.
Removing sod can be heavy work and you wind up losing good top soil along with the sod. If your soil is in relatively good shape, it is possible to leave the grass in place and build on top of it. Place a thick layer (8-10 sheets) of newspaper over the garden bed and wet it thoroughly. Then cover the newspaper with 4-6 inches of good soil. The newspaper will eventually decompose and the turf and weeds will be smothered. There may be some defiant weeds that poke through, but not so many you can hand weed them.
Starting with good soil means you won't have to add a lot of artificial fertilizer to your garden. If you've fed the soil with amendments, the soil will feed your plants.