Hummingbirds need lots of fuel. You can kind of tell by the way they seem to constantly move about very rapidly. And they like to seek out this fuel while they're flitting about.
These birds have a different metabolism than us humans and they also need a significant amount of calories to keep their energy up. Typically, when making food for hummingbirds, you'll want to mimic the sweet nectar of flowers. However, not everything sweet is good for hummingbirds.
Many people have begun to use raw sugar in their hummingbird food mixtures. Seems to make sense. It's healthy for us, we assume it's healthy for hummingbirds. But this is not the case. Like I said, hummingbirds have different bodies than us, different digestive systems and they store and process food differently in their bodies. Raw sugar goes through the same processes as white refined sugar except that certain non-sugar elements remain: Namely, molasses and iron. Hummingbirds' bodies horde iron because they normally don't get it in their diets. Consequently even a small amount of it can be toxic for them.
People also might be tempted to use honey in the nectar they make for these little active birds. Again, honey is also not good for hummingbirds. It can give them sores in their mouths and it ferments quickly; it can mold and be deadly to hummingbirds. Like molasses, it's too heavy for hummingbirds to digest. Agave and brown sugar are also both too heavy for hummingbirds.
Some folks might want to use artificial sweeteners for nectar. These sweeteners don't have enough calories to give hummingbirds what they need.
Many commercial foods contain extra nutrients and flavoring which, essentially, are unnecessary.
So, what should be in hummingbird nectar?