ETBD = Europe Through the Back Door.
Tickets are now electronic. You don't get a paper ticket; just print out your e-mail confirmation of your flight. I also like to put this information on my phone.
You'll be getting an email about 24 hours before you flight, telling you that you can now check in. You should do so online. Depending on the airports involved, you may be able to print your boarding passes from your computer, or may be able to get them on your phone if you have the Aer Lingus app, or may have to wait and get them at the airport (this varies with airlines and routes, and is always changing). So, during the check in process, see what your options are.
At the airport, you will use your passport to confirm your identity and pull up your tickets (if you haven't already printed a boarding pass).
When you get your boarding passes, you will get two, one for each leg (Toronto to Dublin and Dublin to Munich). This way in Dublin, you don't need to stop and get a boarding pass; you merely follow signs to your next gate, possibly passing through security on the way.
People flying back from Dublin to the US go through "preclearance," meaning they go through US customs and immigration in Dublin. However, this doesn't apply to you, since you're flying to Canada rather than the US. So, you'll just change planes in Dublin (passing through security if needed) and go through immigration and customs in Toronto.
As I said in another post, don't worry. You won't be allowed to skip any necessary steps, and no one in the airports wants you missing your plane (just more work for them!). However, at any time if you're lost or unsure, ask for help right away; don't wait to do this.