Nixon took advantage of the Chinese and Soviet split to try and swing the balance of power towards the west by befriending the Chinese.  To do so, he relaxed trade restrictions, made official state visits to China, sent the US Ping Pong Team to China, accepted a couple Panda Bears for the National Zoo in D.C., and also described the "one China" as including Taiwan, a pretty significant reversal of the policies popular previously during the Korean War and espoused by MacArthur and others in the Republican Party who still held out hope of a Nationalist and US-friendly China for a long time.

Nixon, who was known for his foreign policy talents, became the first US President to visit communist China since the 1949 revolution, which gave them some legitimacy in the eyes of the world, and helped to ease tensions between us.

In addition, Nixon hoped that by improving ties with China, he might drive a wedge between China and the Soviet Union, and that they would cooperate less in spreading communism or in plotting against US interests, which worked.  Historians refer to it as the Sino-Soviet split.

What Nixon did was to actually start talking to the Chinese leaders.  He went as far as to actually go over to China to have meetings with them.  Before that, the US had not recgonized "Red China" as a legitimate country.  We had called Taiwan's government the legal government of China.

Through his actions, Nixon created a better relationship with China, leading to us recognizing their government as the legitimate government of the country.

A lot of people see this as the best thing that Nixon did while president.  It improved relations with China and put more pressure on the Soviet Union.