What does "tithe" mean?
Since we are in the New Covenant we are not required to give. However, we don't give because we have to, we give because its our response to how God has blessed us. So we encourage people to tithe, meaning that you set aside the first fruits of your labor/income to the Lord.
We use 10% as a good point of reference for people to aim towards because it is what the bible teaches, but ultimately the Lord wants you to acknowledge him first with your giving (even if it's not 10%).
Tithing, giving God the first 10% of our income to the local church, is the primary, practical way we acknowledge that God is first.
"Honor the Lord with your wealth, with the firstfruits of all your crops; then your barns will be tilled to overflowing, and your vats will brim over with new wine." - Proverbs 3:9-10