Implication and Iff
The Symbols 
and 
Implication:
Implication says "if ... then"
Example:
If both a and b are odd numbers then (a+b) is even
can be written as:
both a and b are odd numbers (a+b) is even
The reason it points to the right is that it might not be true the other way
Example:
Just because (a+b) is even does not mean that a and b are odd (they could be both even)
Iff:
Iff stands for "if and only if"
It is an implication that goes both ways.
Example:
x + y = 3 x = 3 - y
That one is true both ways!