I am on a review of a business process models. I am experienced in UML but not in BPML. The problem I have is that the process models includes user tasks which looks like user actions(from UML) e.g. user press button, user saves, etc. and some technical activities like establishing connection etc.
As far as I know the process model is high level overview and not this kind of granular actions which describes detailed user interactions. Questions:
BPMN covers all aspects of the business and it is meant as a Porsche version of the Volkswagen Activity diagramming. Note: the "Press save button" is not an activity but an action.
BPMN has been developed in order to enhance the documentation of use cases (I'm taking this as synonym for the business process which is not 100% correct but gives the idea) which so far had (more or less) only support in activity diagrams. BPMN's goal is to deliver a complete set of notation which can describe everything related to business, thereby offering the possibility to even document technical aspects, such as timing constraints, exceptions and so on. If you can read activity diagrams its quite easy to read the BPMN notation. However, creating those documents on your own needs practice. It's like the difference between passive and active language.
From the BPMN specs intro:
This specification represents the amalgamation of best practices within the business modeling community to define the notation and semantics of Collaboration diagrams, Process diagrams, and Choreography diagrams.
The current document from OMG is found at BMPN Specs. It's not intended as learning document but as technical specification (mostly for tool vendors). But Google will find you some nice tutorials.