Congrats on the new hobby, and welcome to the (best) club (around)! Your coworkers gave you sound advice, as far as a manageable and approachable start to your running career. Three or four times a week for 30 minutes at a time is a fantastic start to building up your endurance and strength, and will help you build the base you need in order to run farther and faster over time. At first, you might not be able to run those three or four days consecutively. But stick with your training, (making sure you are getting in proper recovery after your runs, plenty of sleep at night, and a well balanced approach to nutrition and hydration) and you will definitely start to see yourself improving, and craving to run on consecutive days.
However, there is not necessarily a standard distance that 30 minutes covers. The number of miles covered in 30 minutes depends on your individual pace. If you are new to running and just starting out (which you are), then you need not be too hard on yourself! Your pace might be slower than other runner friends' running paces. But as you continue to train and run and get stronger, I promise you will also start to get faster. If you are able to run a ten minute mile, then 30 minutes of running would put you exactly at 3 miles.
If you are curious as to how far you are running in 30 minutes, you have several options. The first would be to run for 30 minutes outside, then call a friend to come pick you up, then going back and clocking with a car the exact distance you covered. Another option is to wear a GPS running watch, which tracks time and mileage. This will also tell you how many miles you ran in 30 minutes. The simplest (albeit possibly mundane) way to know what you can comfortably run in 30 minutes is to take to the treadmill. If you have a goal mileage amount in mind, the treadmill can also help you because you can literally set the exact pace you WANT to be running at. If it is easier for you, then that is awesome! If it seems to fast for you to hold consistently, then you know what you need to work toward.