How do I create a mod?

[Astrionix]

I've been thinking about creating some KSP mods for some time but, I don't really know where to start. One question I thought of so far is what kind of application(s) should I use? A couple mods that I've thought of making are parts mods and mods that just change things in the game.

[HebaruSan]

1 hour ago, Astrion said:

what kind of application(s) should I use? A couple mods that I've thought of making are parts mods

For parts mods you only need a text editor to create .cfg files to define your parts.

1 hour ago, Astrion said:

mods that just change things in the game.

Depending on which things you want to change, this may also only need ModuleManager and a text editor to create .cfg files:

Or you might need to write C# code. Someone just asked about that a few weeks ago: