Command line is a program called "cmd.exe". You can start it by pressing WIN+R on keyboard and typing "cmd.exe"
A black window with some text should appear.
Then, you will need to navigate to FH folder using command line. FH folder is usually "C:\FeralHeart", unless you've changed it duaring installation. To navigate on command line you should use "cd" command, like this "cd \FreralHeart" or "cd \games\FeralHeart" in case you've installed FH in "C:\games\FeralHeart". TAB key auto-completes the path. Pressing ENTER key executes the command. If you want to change the disk you are working with, you should type its letter with colon, and press enter key ("C:","D:", "E:", etc).
Once you're in FH's folder, you will need to start FH with special parameters like this: "feralheart.exe >.\runlog.txt 2>&1", where:
feralheart.exe - name of a program you want to start
>.\runlog.txt - redirect STDOUT stream to a file "runlog.txt" in current folder
2>&1 - redirect STDERR stream to STDOUT
This will create a file named "runlog.txt" in FH's folder, containing technical information that may help to figure out why FH fails to start. You may upload that file somewhere, or just paste its contents here.
http://i.imgur.com/TLKcZei.png