How can I know for sure? It is this SIMPLE...

You must first realize that everyone is a sinner…

Book of Romans (Holy Bible) Chapter 3
Verse… [10] As it is written, There is none righteous, no, not one:

[23] For all have sinned, and come short of the glory of God;

 

Realize that there is a price on sin…

Romans 5
[12] Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:

Romans 6
[23a] For the wages of sin is death; …

 

Understand and believe that Jesus paid that price…

Romans 5
[8] But God commendeth his love toward us, in that, while we were yet sinners, Christ died for us.

Romans 6
[23b] ……..but the gift of God is eternal life through Jesus Christ our Lord.

 

Trust him as your personal Savior and you shall be saved…

Romans 10
[9] That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.
[10] For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
[11] For the scripture saith, Whosoever believeth on him shall not be ashamed.
[12] For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him.
[13] For whosoever shall call upon the name of the Lord shall be saved.