Missions in Metal Gear Solid V always ends with a summary, you should take some time to check it. At first the game shows some general statistics and informs you about the number of obtained points. How much points you accumulated determines the received rank (F is the worst, S is the best). More details about obtaining the best ranks can be found in the next chapter of this guide, on the How to obtain the highest S ranks in missions? page.
Another important part of the summary is the screen that shows you the balance of profits and expenses. From here you can learn how much GMP you managed to collect and on what have you spent money. The How to gain money and on what to spend it page will help you in developing well and avoiding bankruptcy.
Other parts of the summary are less important. However, it doesn't mean that they are completely useless. From them you will learn about your heroism score, what additional rewards (like new cassettes) have been unlocked for completing the mission and what new workers have joined your research team.