It’s important to be able to stop when you want to. There are three basic stops in skating: the T-stop, the snowplow stop, and the hockey stop. T-stops are generally easier to learn, followed by the snowplow stop, then the hockey stop.
In a T-stop, begin with a forward one foot glide. Place the back leg behind the skating leg in a perpendicular position and begin putting pressure on the back leg to slow down. At the end of a T-stop, the feet form the letter T. Here is my friend Manny, part-time instructor at Rockefeller Rink, demonstrating the T-stop stop:
The hardest part of learning a T-stop is keeping that back leg firmly behind the front leg. It takes a lot of muscle control. I used to practice "T-drags" to get my back leg in the correct position. Over many practices, my back leg inched closer and closer to the front leg. Here's a demonstration of a T-drag.