While you are at the Civil Registry preparing your application for marriage, you should make arrangements for the ceremony.  It will take some amount of time after you submit the application (like maybe 30 minutes) before you can be married right there in the office, but since you are probably spending a lot of money to have the perfect ceremony, you will have to coordinate with the officer to come to the place where you want the ceremony.  Depending on his/her schedule you may have to wait a few days, but they are very accommodating.

Marriage in the office is free of charge; however, when you want the civil registry office to come to a special location, you will have to pay extra.

The ceremony is short and sweet, and basically you'll just be asked if you take each other to be your spouse and then in the name of the law, you'll be declared united in marriage.  The officer will do all of the ring exchange, etc. per your instructions.

After the ceremony, you will have to get a copy of your marriage certificate from the civil registry.  They will usually give you two copies; a so-called "long" form and a "short" form.  Be sure to have them "legalized" in Mexico, so that it will be completely acceptable back in the US or Canada.  When you get back home, you will need to order certified translations of the Mexican marriage certificate.  Click on the following link to get your Mexican marriage certificate translated:  US Certified Translation Service.

Next  (wedding coordinator)