Just bought FSX Steam Edition + REX4 Texture Direct Twin Pack. How to setup REX4 please?? HELP!

[Cap'n Jack Sparrow]

So I've never played any flight sim before I'm a complete newbie to this. Steam says its installed ok. So I downloaded and ran the rex4 tool. However can someone help me out with the rest please? Don't have a clue what to set in here. I clicked the cog settings icon. It says configuration settings and optimization. But the two browse paths are blank so which path do I set. Also the weather one. Do I have to set a path to a weather directory for the game? Also how do I set up the rest of rex4. I only have the base game with the rex4 config tool. Thanks to anyone who can help me here I'm dying.