I am thinking about converting to Catholicism, but first I want to see what Mass is like. Will I be able to receive Communion? If I don't, what do I do? Am I allowed to enter a Catholic church? Will people give me odd looks because I don't receive Communion? How is Mass different than Protestant services?
Let’s start with your last question. Protestant liturgies generally can be considered praise-and-honor services. There is singing, prayer, and acclamation; Scripture reading and listening to the preacher; and (more or less often, depending on the denomination) a Protestant form of communion, which generally consists of thinking about Jesus while consuming some form of grape juice and some form of crackers. Keep in mind that I am not intending to in any way put down this form of worship. It can be a helpful means of bringing Christians to spiritual communion with Jesus Christ and setting them on the road to a deeper relationship with him. And, in fact, some modern Catholics occasionally put together a similar type of service and call it an agape feast.
The Mass though is an entirely different order of liturgy. It is the sacramental, unbloody re-presentation in time and space of Christ’s sacrifice on Calvary. The person who attends Mass is made present, in a mystical sense, at the foot of Calvary. The closest form of worship to the Mass (in the Christian East it is called the divine liturgy) is not a modern agape feast or a Christian praise-and-honor service; it is the Jewish Passover seder, which is a mystical re-presentation of the Exodus from Egypt. In both services, there is a very real deliverance. For the Jewish people during the Exodus, it is a deliverance from slavery that will foreshadow the deliverance of all nations from sin that Christ would achieve on Calvary.
With this is mind, let’s look at your other questions. Yes, you may enter a Catholic church. All people – Catholic, non-Catholic, non-Christian – are welcome in Catholic churches. Under ordinary circumstances, only Catholics may receive Communion. The rule is not intended to be exclusionary; it is intended to recognize Communion for what it is (the Real Presence of Jesus Christ under the appearance of bread and wine), and to both strengthen and act as a sign of the sacramental communion of Catholics with Christ and his Church. If you decide to become Catholic, you may receive Communion when you are received into the Church.
I can’t predict how people will react to you remaining in the pew while others receive Communion. I can only say that no one should give you “odd looks” or treat you as anything less than a welcome guest. If you notice that some congregants are walking up to the Communion ministers with their arms folded across their chests, that is a signal that the parish you are in gives blessings to congregants who are not receiving Communion. In such a parish, you may do that too if you wish. For more information, I recommend the booklet linked below.
Mass Appeal by Jimmy Akin