Once you decide to sign up for a task, click the calendar day. Another window will open showing the tasks, then click the Sign Up Here button (you can always remove your name from the task if plans change). Save and close out of that window. Be sure to click the red Confirm button at the top right to complete your sign up. You will receive a confirmation e-mail, and also a reminder e-mail closer to the date of your task.
The tasks that show up under each calendar day will include details about that task. For the food items, you will see a list of ideas for what to bring. For the trips to the hospital, you will see the time they like to go and the phone number to call and confirm the evening before. Also, the sidebar to the left of the calendar includes a link called "Location". This will give you their address and other details.
Once you have registered on the site, the easiest way to access it again is through the e-mail that was sent to you. Find either the welcome e-mail or a confirmation e-mail and use the link in that e-mail to get back to the calendar. You should not need to register with a password on the site.
You can also contact the organizer using the link on the left with other questions. Happy Volunteering!