Ukemi is a type of martial arts that actually has an everyday use. The word Ukemi can broken down into two parts. Uke means receiving (the person on the receiving end of a throw) and mi means body.
They are falling techniques. No matter who you are, they will be a point where you will fall down. To minimize the damage, knowing how to properly fall is a must. If you ever went snowboarding, you will know that the first thing they teach you is how to fall properly.
Practicing is easy, just find a mat and throw yourself at it whilst trying to not get hurt. Just keep on practicing and practicing, them you can throw in some rolls and whatnot. Once you are sure you can land like that instinctively, move on to harder surfaces like grass. At some point you will be like a cat and immune to falls, always landing correctly.
Practice makes perfect no matter the activity.