When skating, it is important to have skates that are well sharpened. This means that you should sharpen your skate blades every now and then to restore the edges and remove any light rust. Generally speaking you should resharpen 10-15 hours of skating on indoor ice or when damages on the skate blade are noticed. Outdoor ice is generally tougher on the skates. This means that you need to sharpen more often.
When a skate is pressed against the ice, its edges will dig into the ice. This is what gives you the grip and glide abilities. The grip depends on the angle of the outer edges, the glide depends on the shape of the skate blade underneath. Body weight, skating skill, the contour profile of the skate, and ice conditions (indoor or outside) also effect the grip/glide.

The most common type of sharpening is called ROH (radius of hollow) or hollowness. Here the shape underneath the skate blade is a centered circle arc. This type of sharpening is used by most people, such as ice hockey players, figure skaters and recreational skaters.
Finding a perfect hollowness will require a lot of testing. A general rule used in Europe to find a suitable radius of hollow (in mm) is to divide the body weight (in kg) with π (3.14). An example would be to take 75kg/3.14 which gives 24 mm (then you can withdraw 2-3 mm if you want more bite).
A deep hollowness will be more fragile and less durable then a shallow hollowness. This leads to more frequent sharpening being needed.

It is also possible to sharpen the skate flat. This is mainly used for people performing Bandy, short track, long track or tour skating, i.e. sports where speed is the most important factor.

When a skate has been sharpened to get sharp edges underneath, burrs will arise on each side of the skate blade. Use a hand hone (whetstone) to remove them by pulling it along the sides. Now you will have perfect sharpness!