It is appropriate to wear what you would to a CofE funeral (i.e. smart, black) unless the family has specified a dress code. It's appropriate to bring/send a card. You can also bring flowers, but some families ask for no flowers.
The majority of funerals have a high proportion of non-practising people in the congregation, so the priest will be ready to lead everyone through the responses, when to sit & stand, and probably explain all the symbolism.
It will probably start with the entry of the coffin, with some music. The coffin may be carried by family members or the funeral directors. If the family are very devout, the coffin may already be in the church before the funeral from having had a previous service for the reception of the body the day before. If there is a procession in, you can either arrive before that and stay in your place in the church, standing once the beginning of the service is announced (either the funeral director will ask everyone to stand, or a bell will be rung), or if you want you can join in the procession after the coffin. The closest family members go first, and others slot in more or less according to how well they knew the deceased, but there's no strict hierarchy.
They'll have an introductory bit with placing Christian symbols on the coffin (a cross and a Bible) and blessing it with holy water.
Then there'll be some bible readings. Possibly a sung psalm. The priest will preach a sermon. There will be prayers read by the family (often children).
There'll be the rest of the Mass (called the Liturgy of the Eucharist), which is mainly prayed by the priest and you don't need to do much. There will be prayers you recognise and can join in with, such as the Our Father. Remember to stop at 'deliver us from evil' and don't continue with 'for thine is the kingdom ...'
Communion is next. Usually with a hymn. As pp have said, you shouldn't receive. No one will stop you if you do, but it's not properly allowed. You may receive a blessing, if you wish, or stay in your pew and do nothing. If you want a blessing, you show it by crossing your arms over your body with each hand touching the opposite shoulder. You can do that just before reaching the front of the line/rail.
After communion, there will be a eulogy given by the family. Sometimes one person, sometimes two or three.
At the end, there will be a final blessing of the deceased with incense, and then a procession out with music. You process out with everyone else, letting the immediate family go first. And everyone stands around as the coffin is placed in the hearse.
Since the cremation isn't immediate, people then generally proceed directly to the reception. If you aren't going to the reception, you give your condolences to the family before leaving.
It's highly likely that there will be an order of service booklet with the hymns and readings in. It might also have the Mass responses in, but not often. It will nearly always have personal memories & photos from the family and details of the reception and cremation - which will tell you whether the cremation is close family only or all are invited. You're generally expected to take this away with you (and do what you want with it once you're out of sight), but if you don't want to then it would be fine to leave it at the back of the church.
There won't be a monetary collection during the Mass. Occasionally there will be a person collecting on the way out, for a named charity. More often, there will be a notice in the order of service saying something like 'Family flowers only, please. If you would like to make a donation in X's memory, we are raising money for Y.' (Y is most often a hospice/cancer charity or similar that cared for the person who has died, sometimes a particular cause that the deceased supported). And there will be details of how to make a donation online/by post.
Some families will add personal touches, but that's the outline of a standard Catholic requiem Mass.