I am new to SharePoint and wanted to know if multiple users can access and use a group calendar. I know that SharePoint uses MS SQL to store the data and SQL can be accessed by multiple users. In the unlikely case when two or more users access the same group calendar that is set up for reserving resources, can they all make reservations or will only the first person that accesses the site be able to use it?
SharePoint is a collaboration tool, meant for multiple users to access everything at the same time. Your calendar can be accessed by X amount of users, simultaneously. Individual identities are not passed onto SQL, the SharePoint site's web application pool identity is used to access SQL.