Corr the english mistake

Egypt Museum ^ is ^ in Cairo. [It opened in 1902 --> In 1902, the Egypt Museum started work]. ^It^ is the biggest Museum about Egypt.
Egypt Museum [keeps --> kept] over 250,000 collections about The King of Egypt (pharaoh). Many collections [has existed --> was] many years ago. Some collections [have existed -->is] over 3000 years. The Egypt Museum [has 2 storeys --> have 2 floor]. The collections [ are --> is] following the collections's decade of a century { 我不明白這句的意思, 所以不知怎改}. If you visit [Egypt --> Egypt Museum] {你是想介紹Egypt Museum, 應該不會突然談論 Egypt 這個國家} you can know many things about Egypt's King and Queen.

註: [ A --> B ]: A replaces B
^A^: insert A at there
　｛..｝Expalanatory notes

Maybe you could modify the passage as follow:

In Cairo, Egypt Museum opened in 1902 is the biggest Museum about Egypt.
It keeps over 250,000 antique collections about Pharaoh, the king of Egypt. Some of them have existed over 3000 years. After visiting the two-storey museum, you will know Egypt's King and Queen well.

The Egyptian Museum of Cairo, opened in 1902, is the world's largest Museum of Ancient Egyptian history. It houses over 250,000 pieces of collections of Egyptian Kings (Pharaohs). Most of the collections date back to the last century with some over 3000 years old. The Museum has two floors and the collections are arranged in sections of various decades. The Museum will provide you with a wealth of knowledge about the lavishness of the Egyptian monarchy.