here is my source code :

The question isn't very clear, can you explain what you are attempting to do?

To Run the engine go to : (Your drive letter, my own is E) E:\\Epic Games\UE_4.15\Engine\Binaries\Win64 or there should be a UE4Editor.exe

If you installed Unreal then opening a Unreal project is as easy as double clicking on the project. If it doesn't work use your windows/ oz to associate those files with the editor.

If you build your own Unreal engine from the source then you need to run the "GenerateProjectFiles.bat" to associate the projects.

Source code doesn't open with Unreal. Unreal has no script editor and only has the blueprint editor. To use C++ code with Unreal you need a C++ editor Visual studio is the recommended editor.

The programming guide: https://docs.unrealengine.com/latest/INT/Programming/

Here is the official Unreal tutorials: https://docs.unrealengine.com/latest/INT/Videos/

To build the Unreal engine from source use this: https://docs.unrealengine.com/latest/INT/Programming/Development/BuildingUnrealEngine/

If you never used a C++ editor to build source code then Unreal is not the place to start.

If you are new to building source code then keep a copy, you will need it if you make mistakes.

I know some people like using the source code because it's smaller to download, I just want to point out that with the Epic launcher you can select to only download the core engine, it's less than 4GB and downloads fast. I will recommend installing over source code for most users.

i try to import game source code to unreal. that game have a pak file. i extract it. then have two that folder. i run unreal project file( in 'MyProject2' folder), but it not take file in 'engine' folder. how to import to unreal and run it?

Disclaimer: The pak files should not be used for file sharing! Opening a pak file, without legal permission, can be considered immoral if not illegal.

You are wasting your time, pak files only have assets in them; not the source code for the game. They are a way of storing 3D models, textures, sound and other game content in a smaller and encrypted file.

Even if it has some code, that alone won't be enough to run the game or to open it in Unreal.

The assets in the pak can be imported into your engine like any other asset, making pak extractors a last resort recovery option.

To use the contents you extracted you would need to rebuild the game importing the assets into the game as needed. This won't be a problem if you made the game yourself.

If someone gave you the pak file as a example ask them for the original project file. If you want to reverse engineer a game, you need more than just pak files.

how to import to unreal and run it?

You can't as Scouting Ninja described.

The best analogy I've heard is that the process of building those for the launched game is like turning a cow into hamburger. It is a one way process. You cannot turn hamburger back into a living cow, although you might be able to extract a few useful bits from it.

Trying to get the resources back is foolish at best, illegal at worst. Sometimes it is done in an emergency, like if a game developer somehow lost every copy of their code and needed to extract some things from a product they published, but that is expensive and extremely rare.