Learning to use Substrate is similar to learning to use any other programming library.
In order to do development, you will need both a compiler for your device (provided by the vendor) and the header files and libraries for Substrate.
In addition to Apple's iOS SDK (which will require a free registration on their website), most developers work using a third-party framework called Theos.
Over the years, I've given a number of talks; most of them are long (an hour), but a few of them are sufficiently short that I recommend a quick watch.
In 2010, I was invited to Foo Camp, where I gave a fast (five minute) talk summarizing the state of software modification using Substrate on Cydia.
In 2011, I announced Substrate for Android at the O'Reilly conference Android Open, showing demos of modifying a closed-source Honeycomb tablet.
While there are many more things that could use a good exposition, this website does contain a lot of information about developing with Substrate.
On each supported platform, Substrate offers a way to get your modified code loaded into the processes it wishes to modify.
Whether they actually help out or simply provide a shoulder to cry on, having other developers around when you run into problems is absolutely critical.
This is especially true for new platforms, such as Android; if you don't tell us about the issues you are having, trust us: we don't know about them.