The invasion of Ukraine by Russia provides a good example of just one of the many benefits of the Second Amendment. Many citizens of Ukraine lined up to obtain guns to help defend their country from the invading Russian army. The protection of the right to keep and bear arms helps to keep the citizenry of a country armed to fight and deter possible invaders and to fight its own government should the government turn against its citizens. It also helps to improve the skills and readiness of the citizenry in the use of guns.
Critics say that citizens armed only with rifles are no match for government armies. The armies are much better trained and have powerful weapons that can annihilate the citizens. This is true. But there are reasons why dictators who invade or seek to take over a country are often hesitant to use the massive weaponry they have available to them. For example, dictators by their nature are parasites that live off others. However, they cannot live as parasites if they kill large numbers of the people and destroy the assets—the factories, homes, and businesses—off of which they plan to live. Cultural ties may also limit the type of weapons and the amount of force an army is willing to use. As a result, citizens armed with rifles can make it much more difficult for an army to conquer a nation. Even if the nation is defeated, citizens engaging in armed resistance can make it much more difficult to occupy the nation and may be able to wear down the occupying army.
For more on the benefits of an armed citizenry and how to strengthen the Second Amendment (as well as the discussion of related issues), see the discussion of the Second Amendment in my book A Declaration and Constitution for a Free Society.