on the top, there is a Feather (Post 89)
on the bottom, there is a Sun (Post 4)
A young bird opens its wings under the sun to practice flying, it needs to try again and again to learn how to fly, which is meaning of Practice.
It is an ideogram character.
Its small seal script is
Its clerical script is
It is same as the clerical script.
Its current standard printing script for simplified character is
which is half of the Feather, it may be better to be the simplified character of Feather (羽）. It is not good to be a simplified Practice (習), obviously 习 destroys the ideogram of character 習。So it is not a good simplified character.
Now, 习 has other meanings: get used to, habit - something people need long time to get or become comfortable with.
Its Pinyin is "Xi2".