The sumo deadlift is a really useful movement for building strength in the posterior chain, including the glutes, back and hamstrings, as well as working the core and quadriceps. It is also a great alternative to a regular deadlift as it puts a lot less strain on the back.
To perform a sumo deadlift simply stand in front of the bar with your legs wide and feet facing outwards. You will want to have your shins very close to the bar, but not quite touching. You will then bend down with hands shoulder width apart grabbing the bar. Before lifting the bar from the ground pull your shoulders back and bring your hips as close to the bar as possible.
Stand up driving the knees wide and squeezing the glutes and core at the top. You can then squat back down placing the bar down and resetting, bringing the hips as close to the bar as possible once again.
You can progress this movement easily by adding more weight to the bar.