The fundamental start of any project is a scope of work document, which specifies what we want the project to achieve. The project scope may start out broadly described based upon business objectives, but it will become increasingly detailed over time. Once we have a detailed scope of work, we can produce a work breakdown structure (WBS).
A WBS is a hierarchical disaggregation of a project into small, more readily understood individual packages based upon deliverables. The resulting structure will look like a bill of materials.