Short answers, pulled from the story.
The 1939-1940 Winter Offensive was a major engagement between the National Revolutionary Army and the Imperial Japanese Army during the Second Sino-Japanese War. It was the first major Chinese counter-offensive on multiple fronts of the war.
Chinese commanders believed Japanese forces had grown too dissipated to hold new territory after being repulsed at the Battle of Suixian-Zaoyang and the 1st Battle of Changsha in 1939. During 1939 Japan was also replacing many of its large four-regiment divisions with smaller three-regiment divisions and weaker independent mixed brigades, which encouraged China to plan a large multi-front offensive.
The offensive failed to achieve its original objectives, but later studies describe it as a blow to Japanese forces, whose command had not expected an offensive at that scale. By April 1940 the Japanese army had fought the operation to a halt.
Japan planned to invade Ningxia from Suiyuan in 1939 to install a Hui Muslim puppet state, but in 1940 the Kuomintang Muslim general Ma Hongbin defeated the Japanese and the plan collapsed. Generals Ma Hongkui and Ma Hongbin then defended western Suiyuan through 1940, with Ma Hongbin's 81st Corps taking heavy casualties before repulsing the Japanese.
Chinese forces liberated Kaifeng on the 16th of December after two weeks of fighting, capturing a substantial amount of Japanese equipment. They were soon pushed out of the city again.
The Chinese 4th War Area reported more than 10,300 Japanese killed, while Chinese forces suffered 6,564 killed, 4,595 wounded, and 2,828 missing in the First Battle of Northern Guangdong from the 17th of December 1939 to the 10th of January 1940. The Japanese 21st Army reported only 293 killed and 1,281 wounded in the same fighting, which it called the Wengyuan-Yingde operation, while claiming to have killed 16,312 Chinese troops.