After the Jerusalem council, in Acts 15, some broke away refusing to accept the resolution of the council. They claimed Jesus as Messiah but taught the following:  (Eusebius' Church History, 6:17 and Ireneaus' Against All Heresies, 1:26, 3:11, & 5:1)

1. Denied the divinity and virgin birth of Jesus. Mary and Joseph were His parents.
2. Jesus is not the Son of God.
3. Observance of the ceremonial law was altogether necessary for salvation
4. You can't be saved by faith in Christ alone. You must observe the Mosaic law also.
5. Practice circumcision, and observe the law of Moses, and the Judaic style of life.
6. Refused to acknowledge that Jesus pre-existed, being God, the Word.
7. Observe strictly the bodily worship of the law.
8. Reproach Christians for eating unclean meats.
9. They used only the so-called gospel according to the Hebrews (some say the Hebrew version of Matthew). Rarely made use of the other gospels.
10. State Isaiah's prophecy of "a virgin conceiving" should be translated young woman instead.
11. Reject all the epistles of the apostle Paul, whom they called an apostate from the law.

The Apostle John would not even enter a bathhouse where the Gnostic Cerinthus was because Cerinthus taught Jesus was just a man, born of Joseph and Mary. (Ireneaus' Against All Heresies, 3:11)  Eusebius says their doctrines were spawned by evil demons. Those who believe Ebionite doctrine are not Christians. Ignatius in Smyrnaeans 7 said those that believe the Passover does not refer to Jesus and His death on the cross are not Christians and we should not even speak to them.

A subgroup developed that added to the above:

Did not deny that the Lord was born of a virgin and of the Holy Spirit, but they did deny the divinity of Jesus. They observed the Sabbath and the rest of Jewish lifestyle, but also celebrated the Lord's day as a memorial of the resurrection of the Savior. Some also practiced oaths of poverty and vegetarianism

Later a full Gnostic sect developed: (Ireneaus' Against All Heresies, 1:26, 3:11, & 5:1 and the Pseudo-Clementines)

Rejected any distinction between Jehovah the demiurge, and the supreme good god. Matter is eternal, and an emanation of the Deity This Son of God is the Christ, a middle-being between God and creation, not a creature, yet not equal to, nor even to be compared with, the Father  Man is saved by knowledge (gnosis), by believing in God the Teacher, and by being baptized unto remission of sins.  This system is Pantheism, Persian Dualism, Judaism, and Christianity fused together.

Ebionites seemed to have died out about the fifth century.

References:

Irenaeus Against Heresies 1.26 Irenaeus Against Heresies 4.21 Irenaeus Against Heresies 5.1 Tertullian Against Marcion 1.33 Hippolytus Against Heresies 7.22

Origen Comm. Matthew 6.12 Origen Cel. 5.61 Origen Cel. 5.65 Irenaeus Against Heresies 3.11

The name Ebionite can be translated poor. Some suggest this was applied to James group in Jerusalem, even though a different word is used in Scripture. If this is true it may only refer to the Jerusalem Christians who took an oath of poverty. This could just as easily be referring to people who are poor.

Tertullian states the founder of the sect was named Ebion. Epipanius traces the origin to the Christians who fled to Pella after the destruction of the temple at Jerusalem; 69-70AD, he also adds that some of them held the belief that Adam was an incarnation of Jesus.  Ebionites were found all over Israel and the surrounding region, Cyprus, Asia Minor and even a far as Rome.