Suleyman the Magnificent was one of the most important rulers of the Ottoman Empire. Suleyman was not the first emperor of this empire, but he was the emperor under whom the Ottoman Empire reached its peak size.
Suleyman the Magnificent did not conquer the entire empire all on his own. The empire was started in the late 1200s by Osman Bey. Suleyman only came to rule in 1520, which means that the Ottoman Empire had been growing for over 200 years before his reign. However, in his time, Suleyman expanded the empire greatly. He conquered Baghdad, thus adding that part of Mesopotamia to the empire. He conquered areas in the Balkans and in North Africa. By the time he was done with his conquests, the Ottoman Empire controlled the whole coast of North Africa. It controlled the Nile River region in Egypt. It controlled all of what is now Lebanon, Syria, Jordan, and Israel. It controlled all of Greece and the Balkans and it controlled the areas in the Ukraine that border the Black Sea. In addition, of course, it controlled its home region of Turkey.
Suleyman was able to do this mainly through military power. He is also known for his reforms within the empire. He did things like improving the legal system and supporting arts and culture. However, these things did not really help him to conquer. His conquest was achieved through military (both land and sea) power.