maybe by the level of the '0' and the '1'?
if your questions are brief, the answers will also be brief.
Assuming you are asking how you can detect when the uart receives a '0' and '1'
By sampling the incoming data at a higher rate than the incoming rate, you can detect the '0' to '1' transition or vice versa. If you have enough transitions, you can get a good guess of the baud rate, and thus you obtain your individual bits.
If you know your baud rate, you don't need the learning sequence, and just synchronize on the start bit to find your byte boundary