To add resources to a particular item, please follow the below steps:
You can NOT type straight into the Build-Up Box, but if you double-click on the next blank line then the Resources Window will open.
You can then click on View Library and select the heading that the resource would be in (Labour, Plant, Material, etc).
Once done, you can then type into the search box. Click Enter and the system will filter the result.
Double-clicking on the required resource will then add it to the Build-Up Box.