Covered garden rows help protect plants by sheltering them from precipitation and wind, maintaining optimal growing temperatures, and deterring pesky insects. Garden fabric (AKA floating row cover or just row cover), is the substance used to create rows of tents that cover developing fruits and vegetables.
Some plants can support the fabric directly, others would be damaged by draping cover, so they need frames of some kind to hold it up. These can be anything from simple wooden braces to curved metal or plastic hoops. Secure the fabric with some kind of stakes, like earth staples, so it doesn't blow away.
Garden fabric differs from typical drop cloths in the amount of light it allows to pass through. Where a tarp would block almost all sunshine, leaving shade beneath, good garden cover can admit 70% or more light, nourishing the plants beneath and keeping them cozy. This shelter can be especially valuable for newly transplanted baby plants—the most vulnerable to pests and weather.
Row cover is also designed to admit moisture from precipitation or irrigation, so it can stay in place as the plant develops. Products with greater transparency for light and water tend to have lower heat retention, so they're good in warmer months, but won't protect from frost. Others work the opposite way, reducing light and water transparency by increasing heat trapping to extend the growing season into spring and fall.
Garden fabric should last at least a few years. Keeping it firmly pinned to the earth will help it last as long as possible by reducing wear and tear from flapping in the wind.