"Execution" means putting your signature on it, having it witnessed and having your signature, and the witnesses signatures notarized. Your state laws will dictate how many witness signatures are needed.
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You can only execute files that have the .exe or .msi (for some versions of windows) extension, simply right clicking, then selecting "open" or "Run" should work.
A thread can do anything a regular class does. However, the idea of having multiple threads is so that the computer can do several things simultaneously.