Let's say you're a manager and you need to keep track of what's going on amongst your sales reps at your company. First, make sure you know how to set up the proper permissions to allow this kind of thing, as that will be key. Once you've got permission to edit the contacts of other users and they are sharing their calendar with you, you'll be good to go.
Keeping tabs on the work of your sales reps will be done through the CRM's various reports. Start with the Activity Report--this page is a running list of current activity in your CRM, and can be filtered to see specific kinds of activity associated with specific users' contacts. You'll find the Activity Report under the Workspace tab in your navigation bar at the top of the screen.
You can apply filters to the Activity Report using the "Filter by activity type" and "Filter by user" buttons in the page's header bar. You can also click on the dates next to the "Date Range" in the header bar to filter to activity in a particular window of time.
You can also check individual Pipeline Reports from the top-level navigation -- the names of these reports will vary depending on your CRM's customization, but the most common type is Leads or Sales Leads. (If you have just one type of pipeline, the menu will inherit that name. If you have multiple, the menu will read: "Pipelines.")
By default, each report displays a list of all contacts/companies in the CRM with an attached pipeline of that type that has an active status. You can then use the filters at the top of the report to show only a specific user's activity, along with various statuses or status types (i.e. active or closed).
Staying on top of a rep's calendar is even simpler--just open up the calendar using the link in the navigation bar and you'll see a list of users in the left column with checkboxes by their names. Check the box by a user's name to see their events and tasks on the calendar. You can view just a single user's calendar or all of your users at once, whichever is easier!