For that first error, it seems to be missing a file inside of the engine itself. Could you try verifying the installation through the Epic Games Launcher?
The message “demoGametest could not be compiled. Try rebuilding from source manually” means that there were compiler errors. After doing all of this, could you try compiling again in visual studio and see if the error message you receive is the same? If so, could you also check the Output tab in Visual Studio and copy/paste what is shown there? If there is a lot of it, it may be best to upload it in a .txt file.