if (expr) {
// If expr is TRUE,  do this, then exit the IF loop
}elseif (expr2) {
// If expr is FALSE, and expr2 is TRUE, do this, then exit the loop
}else{
// If all expr's are FALSE, do this, then exit
}

While accurate, there is a shorthand method that does not involve the curly bracket. If there is only a single evaluation, you can remove the curly braces completely. The following two examples are both completely valid syntax for control structures:

if ($a == 1) echo $a;

if ($a == 1) {echo $a; $a=2;}