Catholicism teaches the orthodox Christian faith. In other words, Catholicism is the standard of all Christianity. Other Christians have fallen away from the Catholic Church and have adopted beliefs which differ from those which Jesus Christ passed down to His Apostles and in turn they passed down to us.
What are those differences?
There are lots. So, I’ll give you the two main ones.
1. Sola Scriptura.
That means the Bible Alone. It is a false doctrine which contradicts Scripture. Scripture says we should obey the Church:
And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican.
Obey our Pastors:
Obey them that have the rule over you, and submit yourselves: for they watch for your souls, as they that must give account, that they may do it with joy, and not with grief: for that is unprofitable for you.
And obey Traditions:
2 Thessalonians 2:15
Therefore, brethren, stand fast, and hold the traditions which ye have been taught, whether by word, or our epistle.
Those who teach Sola Scriptura deny all those and thus while claiming to obey Scripture, actually disobey Scripture.
The Catholic Church upholds Scripture and thus obeys everyone of those injunctions.
2. Sola Fide Or Justification by Faith Alone.
Ye see then how that by works a man is justified, and not by faith only.
But believers in Sola Fide claim that we are justified by faith only. It seems an utter and complete contradiction of Scripture. Nevertheless, that is what they believe.
What does the Catholic Church teach on that matter?
We are justified by faith apart from works in the Sacraments. The Sacraments are God's works and we simply believe that He can do what He promised to do in the Sacraments. In Baptism for instance, God promised to wash away our sins:
And now why tarriest thou? Arise, and be baptized, and wash away thy sins, calling on the name of the Lord.
We believe Him. Therefore, when we are Baptized, we are cleansed of our sins according to our faith apart from any works because only God can do that.
However, in preparing ourselves to be justified in the Sacraments, we are justified by faith and works. We thus exercise our faith and make ourselves better disposed to receive the Grace of God in the Sacraments. The Council of Trent explains it like this:
It is furthermore declared that in adults the beginning of that justification must proceed from the predisposing grace of God through Jesus Christ, that is, from His vocation, whereby, without any merits on their part, they are called; that they who by sin had been cut off from God, may be disposed through His quickening and helping grace to convert themselves to their own justification by freely assenting to and cooperating with that grace; so that, while God touches the heart of man through the illumination of the Holy Ghost, man himself neither does absolutely nothing while receiving that inspiration, since he can also reject it, nor yet is he able by his own free will and without the grace of God to move himself to justice in His sight.
Scripture puts it this way:
For not the hearers of the law are just before God, but the doers of the law shall be justified.
Therefore we are justified in our entire life. First by faith and works, when in response to God’s prevenient grace, we prepare ourselves for justification by our repentance, prayers and works of obedience to God. Then in the Sacraments we are washed in God’s sanctifying grace and thus justified by God Himself. All we need to do is believe in His promises - No works necessary.