If you have an uneven backyard and want to put in some sort of surface that will allow you to sit outside, run a grill, and avoid sitting in dirt, a deck is often the most versatile option -- sink some pilings into the ground and raise the surface above all of the rocks and crevices. But not everyone wants a raised deck; there can be stability and weight limit issues, curtailing some uses of the deck. Plus, the extra space underneath the deck can be dangerous if you have little kids who like to escape and run around. If you prefer a patio, you do have ways to make that happen.
One way is to simply excavate the yard and smooth everything out. With the addition of proper drainage and by filling in low spots, you can have a level surface that's appropriate for a concrete patio. You do have to ensure the soil is well-tamped to avoid settling, which can make the patio surface crack and end up with uneven sections, but there are ways to do that (hire a qualified contractor to take care of this instead of attempting it yourself). Excavation works well when the main problem is unevenness due to rocks or minor sloping, rather than a severe slope.
Severe slopes, though, can benefit from terracing. Instead of excavating the whole yard to make it one level, excavate the yard in a series of levels connected by steps or gentle paved slopes. This option is excellent for yards that are very uneven as well as for households that either don't have small children (to avoid fall risk) or who have children who have learned stairway safety. A bonus benefit of this method is that the terraced areas are held up by retaining walls, which stabilize soil that might otherwise erode and wash away.
One more option is the remote patio. If you have a yard that has a flat area away from the house, you can try building a patio there and connect it to the house with a walkway. This is appropriate if you don't need the patio to be right outside the house and if you can install adequate drainage at the patio site. There also need to be areas that can be smoothed out for installation of a path.
Talk to concrete contractors who have experience installing patios to see which options might work well in your yard. There is always a solution.