Recap the above post:
Get there 15 minutes early, so you can park nearby and walk in casually.
Say hi to those who say hi.
No need to touch the Holy Water at the door to the Church part of the building.
Sit.
Pick up the missalette and find the 3 readings from the Bible.
(The readings are labelled: First Reading, Second Reading, Gospel.)
And now.. The Mass.
Mass begins with the ringing of a bell and all stand as the priest enters and proceeds up to the altar. Often, there is a song sung by all.
After the song, when the priest is on the altar (He's not actually ON the altar table, but the front, the "stage area" is called the altar), He says the Sign of the Cross.
You (plural) stand and follow along in the missalette for some minutes Then, everyone sits down. (This is the cue to find those Readings in the missalette.)
Some regularly-dressed person reads First and Second Readings.
Everyone stands up for the "third reading", The Gospel. It is the priest or a deacon who reads it. When he finishes, everyone sits down again.
The priest or deacon gives about a 10 minute sermon.
When it ends, open up the missalette, around page 10 to follow the rest of the Mass, beginning with the Nicene Creed.
Everyone will sit again (just follow the crowd

) and usually there is a song sung as these guys pass baskets around collecting envelopes and money from the people. If you want to put in some, but there is NO obligation. However, you want to feel that you are blending in more, have a folded $1 bill ready for this.
NOW things get really interesting

You will see two or more people approach the altar carring stuff. These are the gifts, the bread and the wine. They hand these to the priest who takes them to the altar table.
He asks God to bless these gifts.
(I won't go through the whole step-by-step, since you'll be sitting there holding amissalette, and I am currently sitting HERE without one.)
Everyone will kneel for the "Eucharistic Prayer". You don't have to; you can sit, but be aware someone is knelling behind you so don't sit WAY back.
There are FOUR Eucharist Prayers. You must pay attention to WHAT are the priest's first words so you can know whaich of the four he is using. (They are all similar.) It is during the Eucxharistic Prayer, while the people are kneeling, that the bread and wine become the Body and Blood of our Lord Jesus Christ.
When the Eucharistic Prayer is over, all stand and pray aloud the Lord's Prayer, the "Our Father". People might hold each others' hands for this, so don't freak out about this. After that, we shake hands with those near us, as a sign of peace.
Then it is back to the missalette and the "Lamb of God".
All sit.
You won't be going up to receive the Eucharist because you are not in full communion with the Catholic Church. Don't worry that this will give you away as a non-Catholic. A number of people don't go up to the altar. Just remain seated. (There may be a song sung at this point.) You can sing along. You can pray; you can thumb through the missalette. You can RELAX in the Lord. Be at peace.
Eventually, everyone will be back in their pews. Many will be kneeling from the time they had returned from the altar.
But when the priest sits, everybody sits.
When the priest stands, everybody stands.
He pronounces "This Mass is over, go in peace to love and serve the Lord." Another song is usually said as he proceeds out.
All the Catholics STORM out. In five minutes the place is rather empty.
You don't have to rush out; there's no fire.
You might want to walk out "last" so that you can do a little lingering in the foyer area, picking up some free literature in the foyer area, if available.
If anyone (and I doubt anyone will) aks you if you're new because they don't recognize you. Say simply,
"I'm just visiting. This isn't my parish." (This does not mean that you are not Catholic. This indicates that you MAY be Catholic from another church, that you're from out of town. It's not exactly a lie because all you've said is that you are visiting, true... and you are not member of that particular Catholic church, true. But, by using the "catholic" word PARISH, you've blended in with the locals, which might make you feel more at ease.
( Don't wear a bikini to Mass, either.

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http://home.inreach.com/mtbearz/Mass.doc