Good that you are looking into this! I did ux design for years, before working with an experienced information architect, who created user workflows that I was simply envious of!
The way I learned was reading up on UML (Unified Modeling Language), which is used by programmers and business systems analysts - just a smidge differently from the way designers use it. They often use it to model programming and logic flows, ux designers use it to model user flows.
Any UML books you pick up will be helpful in forming the framework you will use to communicate with developers, BUT you'll need to do a mental translation to adapt their rigour to a user workflow.
For instance, I always supply a KEY to translate the shapes I use in a flow. Typically the key consists of, at minimum: user action, system response. You can be flexible in the language you choose for shapes and forming the flow, but you should be as consistent as possible across flows so that your audience can gain fluency in reading your design flows.
Tool of choice for workflows (note: PC user here): MS Visio (this program was designed for flows! also can make beauteous wireframes, but bit of a learning curve). Alternative for Mac users is typically Omnigraffle.