This is a subject that has been taught right and been taught wrong. So I will speak from my heart. This is me speaking on truths that God has given me.
First, God has called the first 10% as his period. This is called the tithe, and in Malachi he says when you withhold the tithe you are cursed. Then he says to test him for he shall bless you to overflowing, then he will rebuke the devourer.
"Will a man rob God? Yet you are robbing Me! But you say, 'How have we robbed You?' In tithes and offerings. You are cursed with a curse, for you are robbing Me, the whole nation of you! Bring the whole tithe into the storehouse, so that there may be food in My house, and test Me now in this," says the LORD of hosts, "if I will not open for you the windows of heaven and pour out for you a blessing until it overflows. Then I will rebuke the devourer for you, so that it will not destroy the fruits of the ground; nor will your vine in the field cast its grapes, " says the LORD of hosts.”
This is offerings on top of your tithe. There are some who teach the name it and claim it. God has said that he will give us the desires of our heart when we reach a level of understanding with God’s goodness and are filled with the Holy Spirit. His thoughts are your thoughts, His purpose is your purpose. There is not a selfish want that you will have. You will not be thinking of all that you want. You will be thinking of all that you can give. You will have a heart that breaks when you see people that are without, children that only maybe get one meal a day, and they only get that from school. How can I think of my wants and desires when I see people needing something I take for granted. So, this is what I will say about offerings when God’s purpose for your money overcomes your desire for it then you have reached a point of blessing beyond understanding. God will pour blessings through you, for you understand His heart. God blesses those who bless. Giving is not only about what you get in return. The Joy of giving to God’s purpose will overtake you. Just like the church of Acts. They would and did give everything because it was not about them but about God.
And the congregation of those who believed were of one heart and soul; and not one of them claimed that anything belonging to him was his own, but all things were common property to them. And with great power the apostles were giving testimony to the resurrection of the Lord Jesus, and abundant grace was upon them all. For there was not a needy person among them, for all who were owners of land or houses would sell them and bring the proceeds of the sales and lay them at the apostles' feet, and they would be distributed to each as any had need.
Acts 4:32-35 NASB