Look at ones around you online. Check out their website and beliefs, pick which one suits you and view their opening times. Literally turn up and take a seat, an usher may guide you to a seat usually. You don’t necessarily have to say you’re new to anyone, but some churches, typically smaller ones, ask if there’s any new people to stand and everyone waves to them and then they might ask you to stay after to have a chat or come to the front or stay where you are while everyone pray for you. If they don’t do this and you want to be known, speak to an usher after and explain you’re new and they’ll get into talking about what to do if you like the church and if there’s any services you can join in the church. Because you’re 18, if you pick a smaller church some have a youth service you can ask if people are you’re age but you may prefer the adult one anyway.

Extra: If you don’t know any songs that fine, you can just clap or they hopefully have a screen with words, it’s the preacher/pastors and other service peoples job to run the service so you will mainly be watching so the pressures off.