Most church services include singing, praying and a talk (or sermon). For the singing bit, you might have to read from a hymnbook, a service-
In a "commmunion", "eucharist" or "mass" service the congregation will be invited to come to the front to receive bread and wine representing the body and blood of Jesus. If you accept them, you must consume them. If you do not usually receive them, come up for a blessing instead.
Prayer can also vary from church to church. In some churches, one person may read a prepared prayer from the front of the church with everyone else closing their eyes and bowing their heads in silence. The idea is that while someone else prays you should be listening to what they're saying and echoing their prayer in your mind.
It is also quite common these days for churches to open up the prayer time to everyone present. Members of the congregation will offer up prayers at will from where they sit. Depending on the church, this will be one or two people, or several. The duration of these times of open prayer can vary too, from under a minute to several minutes. (Churches on occasion have special prayer meetings, although they are usually on an evening, rather than a Sunday morning. During these times prayer can last for hours, even throughout the night!)
Sermons (or talks/homilies as they are sometimes referred to), like everything else mentioned so far, can come in different forms. Not only can the length vary from a few minutes to over an hour, but the presentation style and content can be so different too.