Do humans become angels when they die? If no, what are they and were they before us? Do they have their own planet? Any information on angels would be helpful.
No, humans do not become angels after death. It is true that after the resurrection, we will have new, spiritual bodies. "So also is the resurrection of the dead. The body is sown in corruption, it is raised in incorruption. It is sown in dishonor, it is raised in glory. It is sown in weakness, it is raised in power. It is sown a natural body, it is raised a spiritual body. There is a natural body, and there is a spiritual body" (I Corinthians 15:42-44). However, this doesn't mean we become angels. Notice in this description of the church: "But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, to an innumerable company of angels, to the general assembly and church of the firstborn who are registered in heaven, to God the Judge of all, to the spirits of just men made perfect" (Hebrews 12:22-23). There are two separate categories of beings: an innumerable company of angels and spirits of just men made perfect. Angels and men are separate beings.
The Bible states that all things, including angels, were created:
"For by Him all things were created that are in heaven and that are on earth, visible and invisible, whether thrones or dominions or principalities or powers. All things were created through Him and for Him. And He is before all things, and in Him all things consist" (Colossians 1:16-17).
"Praise Him, all His angels; Praise Him, all His hosts! ... Let them praise the name of the LORD, For He commanded and they were created" (Psalms 148:2, 5).
"You alone are the LORD; You have made heaven, the heaven of heavens, with all their host, the earth and everything on it, the seas and all that is in them, and You preserve them all. The host of heaven worships You" (Nehemiah 9:6).
They would have been among the first things created on the first day since Job mentions their shouts of joy at the laying of the foundations of the earth. "Where were you when I laid the foundations of the earth? Tell Me, if you have understanding. Who determined its measurements? Surely you know! Or who stretched the line upon it? To what were its foundations fastened? Or who laid its cornerstone, When the morning stars sang together, And all the sons of God shouted for joy?" (Job 38:4-7).
Since they are spiritual beings, the concept that they have a physical planet doesn't make sense. They are described as beings occupying heaven and that is a spiritual place.
For some additional material, see Angels.