Catalogs provide a great amount of information like flowering, harvest times, mature size based on rootstocks, if the tree you are considering comes with pollination requirements, and much more.
In general, the stone fruits (peaches, nectarines, Stella cherry and sour cherries) take care of themselves. They are considered "self-fruitful," as they are trees that can be planted all alone and you still get fruit. This also is helpful if backyard space is limited.
The next group is known as "partially self-fruitful," which includes European plums, apricots (yes, a stone fruit) and Rome and Golden Delicious apples. While these fruit trees would prefer to be cross-pollinated for better yields, they too will stand on their own if necessary.
The third group will be known as "self-unfruitful" in the catalogs. This is where most of the apple trees fall. Besides the apple, other listed are pears, sweet cherries, and Japanese type plums. This group seems to be misunderstood when it comes to proper cross-pollination. Cross-pollination refers to the need to have pollen from an entirely different variety of the same species. It is carried by pollinating insects to successfully pollinate each variety. This part is critical if your fruit trees are out in the countryside. If the backyard orchard is in a more populated part of the community, any of our flowering ornamental crabapples will serve as that "other variety," as crabapples are a kind of apple.
There also is a bit of confusion on what kind of an apple we will get. That pollen from the flowering crabapple will influence seed, yet the apple fruit will be true to the variety we planted.
There is a fourth group of apple called "pollen sterile." They can receive pollen from another variety and produce apples themselves, yet the pollen they produce will not serve as viable pollen for other apple trees. If you plant a pollen sterile apple, you will need two more different apple varieties for all three apple trees to produce.
Another key point, fruit tree catalogs will suggest a variety that will be in bloom at the same time to assure proper cross-pollination takes place.
While you are browsing the catalog, be sure to pay attention to how hardy the fruit trees are and specifically how hardy the flower buds are. Apples are going to be the hardiest here in northern Illinois. In descending order then plum, pear and sour cherry are moderately susceptible; next are peaches and nectarines, known as very susceptible; and the most cold injury sensitive are apricots and sweet cherry. For example, our recent Polar Vortex temperatures took out the flower buds of apricot, sweet cherry, peaches, and nectarines for sure. Expect some damage to plums, pear and sour cherry.