There are three basic ways to apply finish
Cloth (wiping)
Moderately fast, cheap, suitable for thinner products, little cleanup. Good for oils, oil-varnish blends, thinned varnish, & stains. Control amount by how aggressively you wipe, easy to remove excess material.
Brush
Slowest, most common, suitable for thicker, slower-drying finishes (like varnish), can be used with care for faster drying finishes (shellac, brushing lacquer, waterborne). Can "manipulate" finishes during open time. Some brush prep & clean up required. Suitable for special effects like glazing.
Spray
Fastest to apply, needs special equipment (expensive) and area, not suitable for slow drying finishes like varnish, great for fast-drying finishes (shellac, brushing lacquer, waterborne), best for toners, Gun cleanup when done.