Our hot water went out. How do i find out if our water heater is still good or if something else is to blame?

The water heater appears (visually) fine, it's not leaking or anything, what steps can i take to check to see if it's still functional. What can i replace on it? Is the water heater the only culprit or can something else be the problem. We are going old school having to boil water on the stove to bath, not fun at all especially during these chilly days 8^ ( Thank you.