Hey, As someone who has made a few mods. It takes a decently big skill set to pull off. For example, say you want to modify some value of the game. You need to know where to look in the code, and know how to use the C# programming language.
If you would like to make a new block, you need to know how to model and texture it. If you want that block to have special properties then you will need to understand how the game is written.

What im saying is that its not easy and you need programming and modeling skills that are at least intermediate.
Here is a start if you have these skills: https://www.youtube.com/watch?v=fvUfQLbYeiw

I'm gonna be at Allstate Chorus for the next few days, but when I get back, would you mind helping me learn how to mod? I've never worked with c# before and I want to learn.

Sorry but that is a tad much, I can give you some resources. But I cant teach you how to program, or interact with unity in such a complex way.

If you want to start learning then Id recommend going to a site called Codecademy. It offers a free C# coarse that is very good quality for free. That is how I learned the bulk of my knolage anyways.

On the unity modding side of things, Look around for some tutorials. There are many to choice from that all pretty much go over the same thing.

Lastly, once you have a hang of C# and Unity modding. Then take a look at the FTD modding reference. Its a tad outdated but offers most of the info you will need for FTD specific modding with their interface.

I wish you the best of luck with your mod. Have an excellent day!