The Bible teaches us that we worship the Lord with our money, through tithes, offerings, and gifts. A tithe is is ten percent of our income contributed to the church on a regular basis. When we feel called to give over and above our tithe, we do so as an offering. When you choose to give over and above your tithe, you can direct your offering to a specific area such as missions, building fund, campus ministry or many others.
Each one must give as he has decided in his heart, not reluctantly or under compulsion, for God loves a cheerful giver.
2 Corinthians 9:7 (ESV)
Honor the Lord with your wealth and with the firstfruits of all your produce
Proverbs 3:9 (ESV)