Confusion with the defination of :first-of-type Selector

I am very new to jQuery. I am not getting the below css rule.

:first-of-type Selector - The :first-of-type selector matches elements that have no other element with both the same parent and the same element name coming before it in the document tree.

The above bold part I am not getting. Can anyone help me the above with an example?

Thanks,
Arup