There is a huge community of people using Arduinos and Arduino-compatible boards to create their own inventions, and they tend to share all the instructions needed to recreate their ideas, and take them further, repurpose them or remix them.
Getting Started
To get started, you could work through one or more of the introductory Arduino examples, which provide simple experiments with detailed diagrams, instructions and example code.
To translate any Arduino project to a Shrimp project, you just need to look at the Arduino Pinmapping page which shows you how the pin names used by Arduino correspond to the pins on the actual ATMEGA chip (this mapping is almost impossible to tell from looking at the blue board).
Most of the components to replicate these will be available on hand at any free Shrimping workshop.
If you are already comfortable with code, you could explore the Arduino language reference.
A great set of experiments for early Arduino learners is curated by Oomlout in their ARDX project documentation (also available as a kit intended to be used with an Arduino board).
Getting Inspired
Thousands upon thousands of projects are documented out there, for free, from playful games, gadgets, toys, pranks, right the way through to really serious science stuff like space exploration or atom smashing. Here’s a few places you might go to be inspired, or to find projects which will help you build something you’ve already got in mind.
Instructables’ Arduino Channel (real world projects, with user-submitted instructions)
Hackaday Arduino Hacks (inspiring stuff, but not always easy to copy without help)
Make Arduino Projects (Makezine is a great source of hacks of all kinds, including electronics)
For more specific, detailed questions, such as how to use particular sensor inputs or control various devices and components, you could try…
The Interfacing with Hardware page from the Arduino Playground
…or just register at the Arduino forum.