= is the unary "assignment" operator
== is the binary "equal" operator
a = b will set b equal to a, and then return a
a == b will check if a is equal to b (returning 1 or 0)
and in PHP, it gets weirder, there is
a === b which checks if two things have the same data type also
if (a = b) will return whether b is true
if (a == b) will return whether a is equal to b