For example, the phrase "Hello, my name is Stephen." is this in modern Cyrillic:
Привет, Меня зовут Степан.
In Old Cyrillic the phrase would probably be
Пiвѥт, Мѥнѧ зовѹт Стѥан.
It is a little off because some old Cyrillic letters aren't fully coded yet. Also, old Cyrillic had Greek letters and was very fond of the ъ. Today, the influence of old Cyrillic can be seen in the Cyrillic of Ukraine which holds on to the i.