I prefer buying year-old crowns, rather than growing from seed (which takes more patience than I have). The second year after planting, you can start harvesting spears for two to three weeks, and six weeks the following year. This allows the plants to regain strength.
Your supplier will provide planting details, but — in short — I plant in rows 4 feet apart, with plants a foot or more apart in trenches about 3-4 inches deep — which I dig with my tiller. Once I set the plants in, I till up the paths between rows and rake that loose soil over the plant trenches until the crows become 5-8 inches deep (on the shallow end for heavy soils). That give me a recessed path between raised beds, which I always like.
Then I cover the path deeply with leaves, and mulch the asparagus also with leaves once the spears or ferns arise. This is akin to sheet composting, because the leaves rot every year to feed the plants.
Harvest spears with a knife, just below the soil surface — being careful not to injure nearby spears that haven’t yet emerged. Better yet, just bend a spear until it breaks.
Remove dead ferns in the fall to prevent asparagus beetle infestation. I also drive in stakes along each bed, using thin rope to keep the ferns from sprawling all over as they tend to do. But that’s just me.