First of all, there's a clue in the word "church" that helps us get to the heart of the "true church." The word “church” in the New Testament comes from the Greek word, ekklesia, which means “to call out.” The only two references in the Gospels are from Jesus (Matthew 16:18 and 18:17).

The church did not officially start until the Day of Pentecost (Acts 2), but since the church is based on the person and work of Christ, it really began with Jesus. He is the one who is “calling out” people who will call upon Him for salvation (Acts 4:12; Romans 10:13). All who call on the name of Jesus are automatically members of the body of Christ through the baptism of the Holy Spirit (see 1 Corinthians 12:13).

When it comes to the church, there is the church invisible, comprised by all those who have trusted Jesus as Savior and Lord. And there is the visible church, comprised of those who gather together. Not all members of the visible church belong to the body of Christ, and not all who belong to the body of Christ gather physically in a church.

The bottom line is the church belongs to Jesus Christ (He says so in Matthew 16:18), and if we belong to Jesus, we are part of that invisible church. Of course, the visible church is important as well, because that’s where we worship the Lord, participate in the Sacraments (baptism, communion), learn about God’s Word, and engage in the church’s mission to the world. It’s also where we exercise our spiritual gifts as given to each believer by the Holy Spirit (see 1 Corinthians 12).

So, to answer the first part of your question, "How do I know I'm attending the right church?" you can probably evaluate your church based on some of the criteria listed above. Even then, you need to use spiritual discernment to see whether or not your church (and in particular, your church leadership) is teaching what is true. The way you do that is to know the Bible and "examine" it daily. The church in Berea did this when the apostle Paul came to town, and they were commended for it (see Acts 17:11)