You need Cash so that you can Hire Managers who automate your operations, earning you money while you are not playing.
Also when you reach Goals you earn yourself some Rewards in the way of Briefcases.
You can watch short Ads to Boost your operations by tapping on the TV Boost & Speaker Boost buttons
You can Upgrade your Managers & Products to increase their performance
Once you have Raw Materials on your Workbench, tap on your Workbench Worker for him to begin processing Product.
Once the Workbench has Products completed you tap on your Market Unit Worker to pick up the Product.
Once your Worker has brought the Products to Market you earn your Cash indicated on the top ribbon in the left corner.