A body of believers. The Church is everyone who believes in and has a relationship with the Lord Jesus Christ. We are here to support eachother, encourage eachother, keep eachother accountable- this means being honest with someone who is a member of the "church" even when they don't want to hear it, but need to hear it. The church is called to love God and love others (including and expecially people who do not believe) we are called to serve others and do it with a humble heart looking for no praise or reward. Church is a group of people who love Jesus and unite to make a difference in the world.
The difference between THE church and A church. A church is commonly known as the building that Christians meet at to worship God and hear a sermon from a preacher and socialize. Though not neccessary for salvation, It is important for Christians to find a good Church in their area that suits them well.
Church is, again, not a building. Church is for fellowship (building relationships with other Christians who will help you grow and walk along side of you in your walk with Christ), worship (bringing glory to God, this could be through singing, or serving others, the way you speak, act, or live your life, using whatever gifts God gave you in His name) and digging into the word (reading and studying the bible, disecting it, figuring out what everything means and how it applies to your life). Church can happen any time and anywhere.
"What church do you go to?"
"I go to Bethany Baptist"
"Oh cool I go to Pacific Lutheran Church"
"Church is canceled because of the blizzard, hey lets have church right here!"