Single Vs. Double Quotation Marks

8 people jump in the pool (double quotes)
$var people jump in the pool (single quotes)

Single quotes print out exaclty what was typed out. Double quotes include the varables when printing it out. The example above allows you to see this play out. Since I added a variable of 8 in php as $var the string with double quotes printed 8 and the single quotes did not