You need lots of brackets - eg traffic lights
you put this in B1 so that if a1 is red b1 is stop.
you are saying "if a1=red then I know the answer - it's stop. but if it's not red then it could be either orange or green so I need another if"
you must put the next if in brackets where the "answer if false" should go.
the full syntax is
=IF(logical test,value if true,value if false)