Performing a lookup and bringing in data from another application

Performing a lookup and bringing in data from another application

Hi
I have two applications; Roles and HR.

When a Leaver form is completed in HR, I would like to pull data based on the Job Role Name in the Leaver form and add in Leavers_Instructions.

So the list of Job Role Names is a lookup field from the Roles application.

I am guessing i need to get the Unique ID for the Job Role I need and then use that unique ID to pull the Leavers_Instructions value.

How would I do this??