I've done a bunch of them over the years. They usually last ~ 45 - 60 minutes:
1) You'll be seated at long tables that typically have pitchers of water and baskets with crackers. You usually will also get some pamphlets from the beverage company and maybe some company branded swag. You'll probably have a note card with 3 drinks listed with the recipe and area to make notes
2) Drink presenter will start with background on themselves and presentation on the company.
3) Presenter will proceed with mixing 3 drinks while giving tips / info.
4) As the drinks are being made, servers will bring out small (maybe 2 - 4 oz) samples of the drinks for all to taste.
5) Usually Q&A to close out