Each activity contributes to the value chain by transforming specific inputs into outputs. The inputs could be demand from outside the value chain, or outputs of other activities, while the transformation is facilitated by ITIL practices, undertaken using internal or third-party resources, processes, skills, and competencies.
https://www.bmc.com/blogs/itil-service-value-chain/

Value Streams & Processes
The value streams and processes dimension is concerned with how the various parts of the organization work in an integrated and coordinated way to enable value creation through products and services. This dimension defines the activities, workflows, controls and procedures needed to achieve agreed objectives. What matters in service management is that an organization establishes an operating model that that effectively organizes the key activities needed to manage products and services.
Value streams
A value stream is defined as a series of steps an organization undertakes to create and deliver products and services to consumers.
Structuring the organization's service and product portfolios around value streams allows it to have a clear picture of what it delivers and how, and to make continual improvements to its services. By mapping its value streams, an organization can identify what is critical, what introduces waste and what can be improved upon.
Processes
A process is defined as a set of interrelated or interacting activities that transform inputs into outputs.
Processes define the sequence of actions and their dependencies, as well as describe what is done to accomplish an objective. Processes are underpinned by policies and can be broken down further through procedures which outline what is done, when, and by whom.
https://www.bmc.com/blogs/itil-four-dimensions-service-management/