pseudo class css

.element:nth-child(1)
.element:hover
.element:visited

psuedo element(An intuitive answer):
							keywords added to selectors (which are followed by 
                            colon ':' or double colon '::') which allow to target
                            specific element (or specific part of element).
example:
 you can style the first letter of a paragraph as->  p:first-letter{/*styles*/}

STRONG NOTE:  Keep in mind that  ::first-line pseudo-element  must be applied
			  to block level (elements which break line on use)
			  elements in order to take effect.

A pseudo-class is a selector that selects elements that are in a specific state, e.g. they are the first element of their type, or they are being hovered over by the mouse pointer

button:hover {
  color: blue;
}

A pseudo-class is a word such as :hover that makes its changes
to the selected element by adding it along side the selector 
before the curly braces in CSS instead of inside the curly 
braces.

You can search for a list of pseudo-class online.

The syntax of pseudo-classes:

selector:pseudo-class {
  	property:value;
}