Describe the main features of the Ebionites’ doctrine.
The Ebionites were a sect of early Christians whose beliefs were different than those of what are now called orthodox Christians. Therefore, the Ebionites have come to be defined as heretics who held a false conception of Christianity.
The Ebionites were a group that believed that Christians should follow the Jewish law very strictly. In this sense, they are a group who believed very much in what Jesus's disciples would have believed since Jesus's disciples saw themselves as Jews. This idea, however, was rejected by St. Paul and by the proto-orthodox Christians.
The Ebionites also (and more importantly) did not believe that Jesus was divine. They believed that he was solely a human being who was conceived and born in the normal way. They believed that he was the Messiah and that he followed God's laws more perfectly than anyone else, but they did not believe he was divine.
A good source for more detail about the Ebionites is Lost Christianities, by Bart Ehrman.