Want to import existing sources into Qt Creator

I am a beginner who has never used IDE before.I've been working on C++ challenges in recent months.Up until now, I have compiled and run on MacOS terminals, but debugging takes time, so I thought I would proceed with development on Qt, but when I put .h and .cpp in the Qt project folder, there are many problems that I don't know why, so I can't help it.This is my first time using IDE itself, so I would like you to introduce me to any introductory materials or materials that may be useful for using Qt Creator or IDE in general.

Thank you for your reply. I will write down the steps I followed.
Create a new project
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Select another project & empty qmake Project
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After specifying the directory, check only Desktop Qt 5.4.2 clang 64bit and click Continue
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Select additional Git for the version control system and press the Exit button.
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Add all of the .h and .cpp and .obj that you have developed so far to the project folder on Finder.(Same hierarchy as .pro) (does not include Makefile)

At this point, the files added on the Qt Creator are not displayed.Do I need to set something up?