Once a pipeline has been created, you can add users to work on the pipeline via the “Teams” section of Sales CRM’s settings.
In other words, the creator of the pipeline, or someone with Admin permission, will be able to add members to the pipeline via “Settings” → “Teams” by then searching the Team Members and adding them.
Do note that each pipeline has their own unique teams. This means that every pipeline may have different users that have access to the Pipeline. This could be interesting for companies that have different department using Sales CRM (e.g: Marketing, Sales, IT, CSM, etc.), each with different workflows and processes.
The Teams section of the settings is also where you will be able to manage who can view your pipeline, work on the pipeline, or has Admin permission.
For more information on the settings, you can find the information here: Settings
For more information on Admin vs. Active Permissions, you can find this here: Permission