It's often used to emphasize how terrible something is, and it's a slightly humorous way of saying "from hell."
Here are some examples of how it's used:
* "That was a test from heck! I'm never going to pass."
* "My commute this morning was a nightmare from heck. It took me an hour to get here!"
* "This heatwave is a vacation from heck! I'm melting!"
So, if you hear someone say something is "from heck," it means they're experiencing something extremely bad!