Knife honing does 2 things: it keeps the blade flat and straight. A knife should be sharpened as needed (about every 6 months or so). Ideally, a knife should be honed before every use. Over time the blade dulls and becomes misaligned. Honing a knife is not the same as sharpening, which applies a new edge. Honing just maintains that edge. It appears sharper because a straight edge cuts better.
Some people say diamond dust coated and ceramic steels sharpen knives. My opinion on this -- yes and no. You use a coarse sandpaper to remove paint. Fine sandpaper will not take off much paint but rather smooth it out. Ceramic and diamond steels are so fine that they really just polish off the blade rather than take off enough steel to sharpen. It does sharpen technically, though very little. I personally think a rougher ceramic, like a coffee cup, will sharpen much more effectively.
Unfortunately a honing steel isn't always available. Another option is to use the spine of another knife as a steel. Basically, use the thick and blunt end of another knife and run your blade over it as a steel.