A tithe is the first 10% of your income. An offering is anything you give above and beyond the first 10%.
The Bible says, The purpose of tithing is to teach you to always put God first in your lives - Deuteronomy 14:23 (TLB) Tithing is a reminder that God is the supplier of everything we have. It is also God's personal invitation to an outpouring of His blessing in your life.
In Malachi 3:10 (NLT), God says this: "Bring the whole tithe into the storehouse, that there may be food in my house. Test me in this," says the LORD Almighty, "and see if I will not throw open the floodgates of heaven and pour out so much blessing that there will not be room enough to store it." This is the only place in Scripture where God tells us to put Him to the test. In other words, He's saying, "Go ahead. I dare you. See if you can out-give me."
These are two fundamental questions behind the act of giving. If God is wise, then you should listen to what He says about financial stewardship. If you trust Him, then you should trust him with all aspects of your life, including your finances. So go ahead. Accept God's invitation to put Him to the test. Start tithing faithfully and watch what He does in and through your life.
"Give, and it will be given to you. A good measure, pressed down, shaken together and running over, will be poured into your lap. For with the measure you use, it will be measured to you.” - Luke 6:38