To assign a  Resource Pool to swimlane or step go to swimlane/step properties (1), select "Resource Pool" in Assign Type picklist (2) and click "Add Resource Pools" link (3):

A Resource Pool Search form will be shown (4). Select a Pool (for multiple selection just click several Pools, click again on Pool to de-select) and click "Add" button (5):

Added Resource Pools will be listed (6) under "Assign Type" field. Each Pool can be removed (7) and configured:

Click "Settings" icon (8) to pop up a Resource Pool Configuration form (9). There will be these elements: Pool name (10) that is a link to proper Pool details page, conditions for human resources section (11), conditions for non-human resources section (12):

Click "Add Condition" button (13) to open condition configuration popup (14). Populate required condition Name (15) and Amount (16) fields. Specify Minimal Amount value (17) if necessary:

• Amount is a number of resources that should be taken by system from the Pool and actually assigned to swimlane or step.
• Minimal Amount is the required minimal number of these resources.
• If Minimal Amount is not specified, it will be considered by system as equal to Amount.
• If system will have less available resources (belonging to current Pool) than set in Minimal Amount, then:
  • step will have no assgnees
  • step can't be activated (set to "in progress" status)
  • error will be shown in Progress Component Assignee Tab

Click "+" button (18) to add (optionally) Resource Attribute Requirements (19) to the current condition. Specify logic for Resource Attribute Requirements  (20) if needed. Click "Ok" button (21) to save changes:

In the example at the picture above, system will take Resources matching these conditions:

• 2 resources if available, at least 1.
• Resources should have attribute "Region" not equal to "West" and "North" or should have attribute "Skill Type" equal to "Manager".  

After adding, a condition will be shown in the proper section (23). There can be more than one condition, and  system will search for and try to assign Resources matching ALL these conditions sequentially (all resources matching first condition, than all resources matching second condition (if available), etc.

After Resource Pool has been set as assignee to a step or swimlane, and proper process has been started, system will do the following:

• Check availability of Resources that belong to the specified Resource Pool and match configured Pool conditions.
• Try to take specified nubmer of available Resources from the Pool and assign them to step.

If there are enough Resources, system will show them in Assignee tab of Progress Component  (24). Also, system will list Resource Pools in "Assigned To" column in a Gantt Chart  (25):

If system will not be able to get required number of Resources from the Pool, it will do the following:

• Set step status to Pending (if it is the first step)
• Show a proper message in the Status Reason (27)
• Show "UNKNOWN" instead of set of Resources in the Assignee tab (28)
• Show "UNKNOWN" instead of Resource Pool name in the Gantt (26)

List of resources taken from the Resource Pool at the Assignee tab has the "Edit Resources" icon (29). If click it, a form will be shown under it (30):

Click "Add Pool" button (31) to assign a new Pool to step. A proper popup (34) will be shown. Select a Pool, populate amount(s) of resources and Attribute conditions (if necessary) in the same way as when configuring Pool at the Process Builder (see above), and save changes:

Click "Add Resource" button (32) to assign a new Resource to step. A proper popup (35) will be shown. Select necessary resource in the "Resource" field (36) and save changes. Select a Resource Pool in the field (37) to make system suggest resources for the field (36) from the selected Pool only.

When Resources/Pools are added, the form will contain resources list (38). Resources can be changed (39) or deleted (40) by clicking proper submenu items. Click "close" button (41) to close this form:

If you try to add a Resource Pool that has not enough Resources at all, you will see proper error message (42):

If there is some available resources, they will be shown (43). The link (44) calls a popup that shows small Resource selection form (45). There you can see all resources from the Pool. Hover on Resource status to see the reason why it is unavailable (46):

This reason is a message from Resource Business Calendar.

If the number of Resources in the Pool matches requirements, but there are no available resources for the current date, proper message will be shown (47):

Select another Resource or Resource Pool.