A. There really are no particular obligations connected with hostessing a bridal shower in the way of speeches or ceremony.  The point of a bridal shower is to give the bride a chance to enjoy some private time with the women who are closest to her.  People usually celebrate with refreshments and gifts (and sometimes games), but otherwise the atmosphere of most showers is usually pretty low-key and casual.

Your duties for the day are limited.  You have done the planning, and will do the set-up and pre-party preparations tomorrow.  When guests begin to arrive, you should welcome them and try to make them feel comfortable.  Having something to drink or munch on while they wait for the rest of the guests is always a good distraction and ice-breaker.

When all guests and your cousin are present, you will probably want to "officially" greet everyone. If you haven't provided drinks before, you might give everyone a beverage and then make an official welcome or propose a short toast to begin.  Or if you will eat right away, you can make a few welcoming remarks when guests are seated.

Sometimes at a shower, there are a couple different parts of the event, and the hostess may choose to say a few words to and/or about the bride at the beginning of each (refreshments, activities, gifts, for example) and before the guests leave. But again, there's no set procedure or specific expectation.

All that really needs to be said by you, as hostess is:

~ you are glad that they could be there to share this celebration
~ you wish the bride good luck on her wedding and much happiness in her marriage
~ you hope that the bride and the guests enjoyed themselves

How and when you express these ideas really is up to you, the activities/schedule of the shower, and your relationship with your cousin and the guests.  Keep things simple.  Be yourself.  Be sincere. And relax.   : )