A basic question that we should all have an answer to is "Where did I come from?" There is an answer. We are quite literally the children of our Heavenly Father. In Acts 17:29 we are taught that "we are the offspring of God".
We existed in a world of spirits with our Heavenly Father, Jesus Christ, and all mankind. However, once we reach this Earth, we forget where we came from so that we can learn by finding our way, through faith, study, and prayer. Jesus Christ taught the prophet Jeremiah that "Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee" (Jeremiah 1:5). The same applies to all of us, the Lord knew us before we came here.
"Even before they were born, they, with many others, received their first lessons in the world of spirits and were prepared to come forth in the due time of the Lord" (Doctrine and Covenants 138:56). We learned all that we could learn in the world of spirits, so Heavenly Father created a perfect plan to accomplish his purpose. commissioned the creation of the Earth so that we might continue our learning.
We are here because we chose to follow that plan. In the scriptures this plan is referred to by several names such as the Plan of Salvation, the Plan of Happiness, the Plan of Redemption, and a Merciful Plan. Jesus Christ is central to the plan. Through the Atonement of Christ, we can all be forgiven of our sins and be made pure again, so that we will be able to once again live with our Father in Heaven.
I know that we did live together in the spirit world before this life. I know that I am a child of God and that he sent me here with a purpose and a plan so that I might learn his gospel and return to him. I know that this is only possible through the plan, which centers around Jesus Christ and his Atonement. I know that Jesus Christ took upon himself all sins, so he might serve as my mediator, that I can be made whole again. I know that a merciful Heavenly Father and his son Jesus Christ live! I know that they know me personally and I know them personally! I know that I love them deeply and they love me deeply! I know that I, like the Prodigal son, can repent of all of my sins, and God will welcome me back into his presence with open arms. I know that these wonderful blessing are available to everyone. Of this I testify, in the name of Jesus Christ. Amen.
Please also watch Isaiah's testimony about where we came from.
Also, please watch Debbie's testimony about the pre-existence.
Next: Why Are We Here?