Hello there. So, I have a lot of places in my composition, when the volume goes over 0db. In my opinion, it's because of frequencies' clashing. I trying to use equalizer, but sounds becomes less brighter or just ruines. Am I need to mess with EQ some more time or just put a limiter on master section (as I did with my previous tracks, but I want to become more professional, and I think just putting a limiter hides the problem, but not solves it)?

Turn the main volume fader down.

What he said ^.

If you then find the volume to be too soft, you need a limiter. All commercially published tracks are compressed & limited to smithereens in the mastering process. Do not compare the volume of your unmastered tracks to commercial releases. Just turn down the master fader of your DAW and turn up the volume of the monitors.

Do not turn the master fader down. That should always be at 0dBFS. Grab all of your tracks at once and turn them down. That way it preserves your mix, and gets rid of the master track going over.

No need to turn down every track (although if you'd been careful with their levels you wouldn't have this problem) - just turn down the Trim/Gain on your master bus, or the Input Level fader on your limiter, and then let the limiter make up the difference.

The reason you can get away with this is that most DAWs work with floating-point data internally, so going over 0db prior to the final output does not cause any problems. You just have to make sure the output of the final limiter is < 0db, and that the peaks going INTO the limiter are no more than -3db (-6db to -12db is better) so that the limiter has some headroom to work with.

One idea is to side chain a compressor on the less important track so it ducks when the other plays. At any one time there should be one main instrument that the audience is listening to (excluding the general drum rythm). If you consider that and go through your track determining at each point which instrument it is then you can duck or automate the volumes of the others that clash.

This!

Moreover, learn to gain stage correctly from the start.

Keep your master fader at 0. How would you monitor if you didn't? Turn down all your tracks instead. Yes most DAWs work with floating-point data internally, but some plugins don't work as well when pushed. In fact most effect plugins were better with lower inputs. Some of these plugins introduce distortion maybe not heard until limited.

like everyone has said, the easiest way is to turn each part down

Thanks for the answers.

+1000000000

Far too often people think they need to redline everything so they can be part of the loudness war

Maybe that's the proper way, but do that with your next track. Just turning down the master fader will give the same result, and won't mess with your current balance & volume automation curves.
It only matters if you have effects on the master bus post-fader that depend on the incoming volume (dynamics effects with a threshold)

What if you are about to send a demo to a label? Wouldnt you want your track to be as loud as possible?