I need to learn how to build custom workflows in SharePoint. In addition to basic stuff like having legal sign-off on documents, I need to be able to execute arbitrary custom code at certain points. For example, after legal signs off it should export the document and update a database table indicating that a new version is ready.
Is this possible using SharePoint? If so, where can I find the documentation or tutorials I would need to get started?
Getting Started Link 1,Getting Started Link 2 links will help you to get started with the SharePoint Custom Workflows. And also it is possible to do any arbitrary code inside the workflow. Also there is another type of work flow called State machine for which there is a class one article
Workflow as the whole is built using sub parts called Activities which dictates what the workflow should do at a particular point of time, I remember you have an activity called Code Activity which will help you to achieve what you want.
Robert Shelton's Workflow Video Tutorial series is very helpful: