WD-40. Spray it on, wait overnight, repeat, and then perhaps repeat some more. Brush the exposed threads with a wire brush. Find a wrench that fits the nut and tap it frequently and gently. Repeat the WD-40 treatment.

1. Liquid Wrench - good suggestion.
2. Box End Wrench - excellent suggestion
3. Gas Torch - good suggestion

WD-40 is a vegetable oil - very sad distraction

U.S. Material Safety Data Sheet information, are:

• 50%
  "aliphatic hydrocarbons". The manufacturer's website claims this ratio
  in the current formulation cannot accurately be described as Stoddard
  solvent, a similar mixture of hydrocarbons.

• <25% petroleum base oil. Presumably, a mineral oil or light lubricating oil.
• 12–18%
  low vapor pressure aliphatic hydrocarbon. Reduces the liquid's
  viscosity so that it can be used in aerosols. The hydrocarbon evaporates
  during application.
• 2–3% carbon dioxide. A propellant which is
  now used instead of the original liquefied petroleum gas to reduce
  WD-40's flammability.
• <10% inert ingredients.

You can probably put some oil onto it and then try to remove it.

Omg I’ve tried evvverryything, someone came over and took a look for me and they said they have to be cut off so he’s ganna help me today! I don’t think I’ll ever take on a bench as a job again! What would someone charge for a job like this? Maybe I just feel like it’s not worth it right now cuz I’m new to this lol.

Bernz-O-Matic.

Thanks, I’ll keep one around for future but I don’t wanna practice with it on my first ever “job”

Kroil. It’s amazing what it can loosen up. And a good set of real tools. A socket set gives you more leverage than a box wrench.

http://www.kanolabs.com/google/?gclid=EAIaIQobChMIptqIvLaw3AIVEL7ACh182Q_cEAAYAiAAEgIO3vD_BwE 

I bought two socket wrenches and a friend came over to help with his set and they won’t come off.

Then either the torch or failing that, angle grinder. Use galvanised bolts and nuts when you put it back togeher..

I had to cut them off, how do I know what size it is to buy new? I’m at a store right now and no one can help me.

You need measure the hole diameter (or diameter of the old bolts, and the length. Get galvanized: They won't rust as fast.

Get thee to another store!

If I had to guess on size, I think 1/4" diameter, 2-2 1/2" long will do.

Thank u everyone for ur help ur really helping me learn here! Now, what do I do about these bolts that won’t come off the wood even tho they’ve been cut off?

Pound it through with a hammer.

Or better, hammer enough to get the head out a bit then use whatever means (pliers. etc.) to unscrew them out. Probably doesnt matter but you will minimize damage to the wood that way.