TAG Selector
Used for Tags only (Tag name + Property)
Example:
P {color:#960}
h3 { background-color:#099}

Class Selector (Create a User defined css rule)
Used for Many Items ( use the class name you created + the property
Example: 
.bold { text-transform:uppercase; font-style:normal; font-weight:bold}

To use it:
<p class="bold"> Introsplash </p>


ID Selector
Used for 1 element (use the hash tag when creating: #mainTitle + property
example: 
#mainTitle { font-size:24px}

To Use it:
<h2 id="mainTitle"> Introsplash 2 </h2>


Grouping Selectors

p, h1, h2, h3, h4{ color:#960}