Rest assured that all of us have gone through this and have had the same frustrations. It's not so much about learning how to use this simulator, but in fact, learning how to fly! (see the post by Eclipse above).
If you accept that there is a lot to learn and find accomplishment in incremental achievements then you'll have a much more rewarding experience.
Stick to a specific discipline (helicopters? modern jets? WW2 props?), then stick with a specific aircraft and learn all the different aspects of operating it (avionics? VFR navigation? aerial gunnery?). Eventually, it will all come together and you'll be completing missions using the multi-disciplinary skill-set you've developed, and that, good sir, IS THE GREATEST REWARD OF ALL! ;)
Then later when you switch to a new aircraft, be ready to start the process over again. One of the most wonderful aspects of flight simulation is there's practically no end to the things you can learn! :)