eosacro has been posting some introductory looks into the key components of using SideFX Houdini. Here, he takes a super quick look at Houdini Expressions and Variables, showing how to create simple transforms on an object in the scene.
This is really meant as a quick taste to get you creating Houdini expressions to drive attributes, and offer areas where you can explore further.
There are some other resources for learning Houdini Expressions that we have come across in the past. SideFX Posted a look at Getting Started with Procedural Animation & Expressions Houdini, that took a more in-depth look at Expressions.
Matt Fournier also offered an introductory look at writing Houdini expressions in an effort to help new users get started with the post Expressions in Houdini for Beginners.