Scratch

Here are some tutorials

.:Squeak:. by nXIII
This is the most complete tutorial in squeak that there is. But, it teaches you the latest version of Squeak, Scratch definitely does not use the latest version. This tutorial also is more about Squeak, than it is in modding Scratch.

Squeak - A step-by-step beginner's tutorial by LS97
This is a good tutorial. Especially for beginners, like you. I haven't really checked this one out, but it's made my LS97, so it HAS to be good.

Cool Source code tricks... by billyedward
This is based on little tricks you can do that help to make a mod. It is good, and it teaches you how to do cool things.

Cool custom blocks in Scratch by LS97
This is great for learning how to make blocks. Although, that is NOT what modding Scratch is all about, if you want to make at least a legitimate mod. This thread has a GREAT place for learning blocks.

About stealing blocks... by henley (me!)
This is not about making, blocks, mods, etc. But it does teach you about giving credit, and what to do if you are in troubling stealing/credit situations. It is good for learning how not to tick someone off and start flame wars.

Squeak (Source Code) Guide by johnnydean1
I haven't read this one, but I know it is more about modding Scratch than using Squeak.

Hope it helps!