If you play tennis on Mondays, Wednesdays, Fridays and Sundays, then you are said to play the game on alternate days. In other words, you don’t play every day, but on every other day. The stress is on the first syllable ‘al’.
Example: Wouldn’t it be nice if we had school/college only on alternate days?
The word can also be used to mean ‘one after another’; when things ‘alternate’ they take place in turns.
Example: It was a movie that made you laugh and cry alternately.
The word ‘alternative’ means one or the other; it is normally used to refer to a situation when a choice has to be made. The stress in this case is on the second syllable.
Example: There’s something wrong with the car. Our alternative is to take a bus.
Careful users of the language sometimes argue that this word should be used only when there is choice between two things. This however, is no longer true. You can have several alternatives.