Settings
First, decide how you want this to work. It can allocate from:
Any Location
A specific Location (including sub-locations)
The item's default location
You can also set whether the pop-up box appears when you are manually running this process.
To set these, go to the Cog -> Inventory & Item Management -> Stock -> Default Allocation Method:
Job/Order or Work Order
On a Job/Order or Work Order, click on the Apply button and select 'Allocate All'.
You can then set the method for all (and click the green '+' to apply to all the items), or set a specific rule or location:
The system will allocate what it can and this screen will show you any that have failed.
Automation
Setting this in an automation will obviously not allow you to select these during a run - for each item, it will either allocate or not.