While most cameras now let you compose your shots using an LCD screen on the back, there are lots of times when a regular viewfinder is still preferable. For many people it’s more natural to put your eye to a viewfinder eyepiece than it is to hold the camera at arm’s length. Viewfinders are also more useful in bright light, when glare often makes it hard to see what’s being displayed on an LCD screen.
Viewfinders come in different types. Some older cameras have ‘direct vision’ viewfinders, digital SLRs have optical through-the-lens viewfinders while mirrorless cameras use electronic viewfinders.