Qual è la differenza tra effort e endeavor e exertion ?Sentiti libero di rispondere con un esempio.

effort = more common, more natural, more generic. Could be lifting something but could also mean memorizing phrasal verbs, etc.

That job required a ton of effort!
If you want to succeed, you have to make an effort.
That project was a massive effort for all involved!

extertion is similar but sounds (in my opinion) more physical. eg Lifting something heavy.

You could see signs of exertion on his face as he tried to lift the car.

endeavour is closer to 'proyecto' or 'cosa que hacer'.

A very common phrase when someone leaves a company: "Good luck in your future endeavours". It's very generic, it can mean proyecto, trabajo, estudios etc.

"That was a big endeavour!" sounds like a project, maybe building a house.