A short video:

To schedule a bulk SMS campaign,

1) On the dashboard click on Campaigns under the Tools section on the left,

2) Click on the SMS  button,

3) You will need to fill in the Campaign name, List of contacts, Date, Time, Choose an SMS template that needs to be sent out and click on continue,

4) Select Caller ID(Sender ID) Save the campaign by clicking Add,

Voila! You are done.

PS, This page has more information about how to create SMS templates.