All Christians are welcome at the communion table (where you may also stand or kneel). We use real wine, because that's what Jesus used, but if you do not wish to receive the wine, please cross your hands over your chest as the chalice goes by. If you need gluten-free bread, say so and you will be given a gluten-free wafer.
The more you worship, the more comfortable it becomes. Today's churches are part of one great universal Church, whose fellow members come from all nations and from every one of the past two thousand years. While we can't see them, these members of the whole church join in our worship with us, as do angels and archangels and all the company of heaven.