To forgive means to cease to feel resentment against (an offender) : pardon . In most cases this is easier said than done. Sometimes people do hurtful things to one another and that may cause bitterness, resentment and a loss in trust. The Bible says that a man or women’s enemies are those of their household (people you love and trust). When these people hurt you this is called an “inside attack”. When you are hurt by a stranger or someone that is not close to you, we call this an “outside attack”. Both inside and outside attacks can be damaging to you short term and long term and you need God’s help so that you can get healed.
Peter, one of Jesus’s disciples asked Jesus about forgiveness. This is what Jesus said to Peter and he is saying the same thing to us today.
Matthew 18:21-23 AMP
 Then Peter came up to Him and said, Lord, how many times may my brother sin against me and I forgive him and let it go? As many as up to seven times?  Jesus answered him, I tell you, not up to seven times, but seventy times seven!
When you don’t forgive those that have sinned against you, that gives them power over you. And you end up in prison in your mind. Which leads to bitterness, hatred, resentment and other things.
But if you are willing to forgive but don’t have the strength God will help you if you ask him. Pray this prayer, Father God I come to you in Jesus name seeking your strength and help in time of need. I have been wounded and deeply hurt by (the offender) and I am unable to forgive him/her in my own strength but I am willing to forgive this person and therefore submit myself to you. I am asking you to give me the strength to forgive by using your power on my behalf. Father I thank you for delivering me from all resentment, bitterness and anger against this person and restoring to me the peace of God that passes all understanding, in Jesus name I pray Amen. Now you have released the offender from their sins against you and took back the power they had over you. You are free to serve the living God and savior Jesus Christ. Hallelujah! Hallelujah! Praise God!
Matthew 6:14-15 AMP
 For if you forgive people their trespasses their reckless and willful sins, leaving them, letting them go, and giving up resentment, your heavenly Father will also forgive you.  But if you do not forgive others their trespasses their reckless and willful sins, leaving them, letting them go, and giving up resentment, neither will your Father forgive you your trespasses.