I can "sharpen" a knife if it needs it.
To sharpen a knife, you must remove metal from both sides of the blade at a consistent angle until the two angles meet.
But a knife doesn't need to be sharpened all that often if you understand how the edge really works.
See, under normal use, the edge of a knife doesn't really "dull" as much as you think.
What it does is kind of fold over, so the sharp part is leaning away from what you are trying to cut.
This can be fixed by simply folding the edge back into a straight line. This is called "Honing" and it is why a "Honing Steel" is called a "Honing Steel"
You don't sharpen a knife with a Honing Steel because no metal is being removed.
With a honing steel, you are simply pushing the sharp blade back into a cutting position.
Understanding how and why to "hone" a knife makes a big deference in how you treat it.
I hone my pocket knives about once a month depending on how often I use them.