How to monitor web apps?

How can I use a UiPath robot to monitor the web pages opened by the user and when the bot sees certain fields on a given page it inserts data from another source? I can easily do this as an automated process but how do I get it to sit and continuously monitor for the right page being open? It sounds like it should be a ‘background process’ but that can’t have UI activities? What aspect of UiPath or am I missing?