From the Imperial Household Agency.
Article 1 of the Constitution says that the Emperor is the symbol of the State and of the unity of the people, and that this position comes from the will of the people, with whom sovereign power lies.
A symbol is something that shows an idea we cannot see. Saying the Emperor is the symbol of Japan means the Emperor is a symbol that brings the country of Japan to mind.
The Emperor does only the acts in matters of state set by the Constitution (Article 4). Some of them are:
to appoint the Prime Minister named by the Diet; to appoint the Chief Justice of the Supreme Court named by the Cabinet; to proclaim changes to the Constitution, laws, cabinet orders and treaties; and to announce general elections for the Diet.
During the Kamakura, Muromachi, Azuchi-Momoyama and Edo periods, when shoguns held power, the Emperor was based in Kyoto.
In 1868 the Emperor moved from Kyoto to Edo, which was renamed Tokyo. Since the Meiji era, each era has been named for an emperor.
There is no single right answer. Talking it over with someone at home is a good way to learn.