Why do i need a water softener? and what exact is it?

i am from an area that doesn't use water softeners. never even heard of them before. so i moved to the San antonio area and the house we bought has pluming for one. i hear people talk water softeners but i have no idea what they are for and why i would need one. the guy at sears tried to explain it but... show more i am from an area that doesn't use water softeners. never even heard of them before. so i moved to the San antonio area and the house we bought has pluming for one. i hear people talk water softeners but i have no idea what they are for and why i would need one. the guy at sears tried to explain it but basically said it doubles the life of my water heater. that isn't cost effective if they need to be replaced every so often.

the water in my area has just been named one of the best in TX. we drink straight, and it taste good.

so can anyone explain what a water softener actually does... and please don't say it softens the water. cause i have no idea what that means.

do i really need one???
Update: everyone is being so helpful. yes they say i have "hard" water. but i don't notice any extra soap usage. my skin seems a little more dry but lotion taks care of that. the main thing is the film the dish washer leaves. does not haveing a softener bad for my house? if i get one for the house, is the... show more everyone is being so helpful. yes they say i have "hard" water. but i don't notice any extra soap usage. my skin seems a little more dry but lotion taks care of that. the main thing is the film the dish washer leaves.

does not haveing a softener bad for my house? if i get one for the house, is the hose water outside not effected? what is the upkeep? adding salt?