How do I apply for a visa if I want to travel independently to Singapore, Malaysia and Thailand? Do I need to apply for a visa for three countries?

As long as you go abroad, you need to apply for a visa, unless it is a visa-free country. Singapore, Malaysia and Thailand are not visa-free countries, so traveling to these three countries requires a visa.

A visa (visa) is an endorsement or stamp by a country’s sovereign authority on the passport or other travel documents held by its own or foreign citizens to indicate that they are allowed to enter or exit the country’s territory or pass through the country’s territory. It can also be said to be an endorsement certificate issued to them. In summary, a visa is a document issued by a country's entry-exit management agency (such as the Immigration Bureau or its embassy or consulate abroad) to express approval of entry to foreign citizens.

A passport is proof of the holder’s nationality and identity, while a visa is a permission certificate issued by a sovereign country that allows foreign citizens or its own citizens to enter or exit the country or pass through the country’s borders.