Being able to share calendars and contacts is on of Outlooks greatest strengths. The process to share your calendar and contacts is essentially exactly the same, so we'll walk through sharing your calendar to show you how to do it.
Open up your calendar in Outlook. Now click "File", then "Folder" in the File menu.

Click "Sharing...".

Click "Add..."

This window works just like the Global Address Book. Find the person you want to allow to access your calendar. Click the "Add ->" button for each user. Click OK.
The people you just selected should show up in the "Calendar Properties" window. For each new person, we want to set the level of access they will have. Select the user(s) you want to edit. Click on the "Permission Level:" box, several permission levels will appear.

For most people, the "Reviewer" level or the "Publishing Editor" will make the most sense.
Reviewer - read only access to the calendar.
Publishing Editor - read and write access to all elements on the calendar. A Publishing Editor can create new appointments, edit appointments and delete appointments.
Once you have set the approprate permission levels to each person, click OK.
As I mentioned above, this procedure works the same for contacts.