First thing to do is trip the emergency release mechanism and see if the door works OK manually. Can you easily lift the door up, does it stay open, and does it seem to work smoothly up and down. If so then proceed to repairing the opener.
Very likely the main drive gear in your opener has failed, the gear is plastic and a very common failure. You can confirm this,
Unplug the opener first!
Then you can remove the cover, you will likely see lots of white shavings inside, if so the shredded gear is the culprit. The plastic gear kit can be purchased for around $10-20 depending on how much else is wrong. Sometimes the shaft and upper sprocket bushing are worn too and can be purchased all in a kit, this could also be part of your problem.
If you need to hire someone to do the repair; it will likely be cheaper to just replace the opener. Either way it is not a difficult job if you have the mechanical ability and some basic tools.
The gear set can last many years on a properly working door, or it can be destroyed in just a few weeks on a door that catches, binds or is improperly adjusted. They often do fail for a reason.
Many other brands are identical, Liftmaster, Chamberlain, Sears, Master Mechanic, Do it best brand openers all use this very same design.
Here is just one of many videos on Youtube detailing the procedure: