If you want to sign up online, you can go to https://www.redcrossblood.org/. On this Web page, there is a box in the upper right corner with the title "Find a Blood Drive".
In this box, type and enter smoth. It will find the blood drive on the upcoming dates and display them on the left side of the page. Click on the button for the search result that says "SEE TIMES."
It will then show the times that are available. Just press the button with the time on it you want that says "Blood."
If you are comfortable using an iPhone or Android phone, it is recommended to install the Red Cross blood donation app. You can not only make an appointment from the app (instead of doing it like per above), but the app will also have your donor ID card, and can be used to answer health questions on the day that you donate blood, instead of needing to do that when you arrive (this is called RapidPass). More information about the mobile app is available here https://www.redcrossblood.org/blood-donor-app.html.