Depending on which accounting methods are used, there are different ways to calculate this number. Regardless of how you calculate it, it needs to be a solid number. Some companies may run a negative revenue and there must be a solid reason as to why before going further. When looking at revenue, you may hear it referred to as top line in quick conversation.
Revenue can also be divided up into items such as operating revenue and this can give you different perspective on the company. For public companies, you can find this number quarterly and monitor is throughout the year. When evaluating a company there are many other metrics that are valuable that go beyond revenue. Net income, debt, and assets or others depending on the company. Keep it in perspective too because if the company is new and growing, their revenue may not be the same as a well established company. Look into the ratios that utilize revenue and go from there. You may find a few data points that help to grow you researching knowledge and give you that edge in your investing and trading.