"Just showing up at church" may not seem like much to you - but it shows others that God is important to you, and is a good example to them. It also gives you an opportunity to learn more about God's plan for your life, and to grow in your faith in Christ.
But your church is important for another reason: It's a good place to find opportunities to serve God. Almost every church I know depends on volunteers to help carry on its ministry - from singing in the choir or keeping the nursery, to leading a Bible study or helping in the church office. Your church may be involved in community projects also that need volunteers. Check your church bulletin for openings, and let your pastor know also of your willingness to help.
But you can serve God in other ways also. All around you are people who need Christ, and need to be touched by His love. Are you praying for them, and are you asking God to help you reach out to them? A sick neighbor ... a young person who needs encouraging ... a lonely elderly person - the list is almost endless. The Bible says, "Therefore encourage one another and build each other up" (1 Thessalonians 5:11). Jesus said, "Whatever you did for one of the least of these ... you did for me" (Matthew 25:40).
Ask God to show you the gifts and abilities He has given you. Then ask Him to show you how He wants you to use them - and He will.