There is one God, eternally existent, Creator of heaven and earth. He is manifested in three person; Father, Son and Holy Spirit.
The Bible says:
For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one
I John 5:7
The Lord Jesus Christ is fully God who took on flesh and dwelt on earth. He was sinlessly perfect and gave Himself as a substitutionary sacrifice by shedding His blood and dying on the cross; He then cam back from the dead. This was to pay for all sins (past, present, and future) for all who believe.
The Bible says:
By that will we have been sanctified through the offering of the body of Jesus Christ once for all. And every priest stands ministering daily and offering repeatedly the same sacrifices, which can never take away sins. But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, from that time waiting till His enemies are made His footstool. For by one offering He has perfected forever those who are being sanctified
Hebrews 10:10-14
Man is saved by undeserved mercy through faith and nothing of man enters into his salvation. It is a free gift. Salvation is by the finished work of Christ and nothing can be added to it.
The Bible says:
For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast.
Ephesians 2:8-9
The Bible says:
Not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit
Titus 3:5