What are tags?
Tags are keywords or labels that you add to people, organizations, events and documents. You could tag a person with "Employee" and then tag everything else which's Employee-related as "Employee". Later if you look for anything to do with employee, you can just click that tag and get all the stuff that have been tagged that way. Tagging is all about stuff make sense to you.
Can I add tags without people / organization / events / documents?
Nope.
How do I delete a tag or rename it?
Can you give me some suggestions for tags?
Sure. Basically, there are 2 types of tags, including abstract and concrete respectively (e.g. 'human' is abstract and 'Jason Smith' is concrete).
Abstract tags are commonly used for categorizing stuff. For example, you can use 'customers', 'suppliers', 'employee', 'candidates', and 'friends & family' to orgnize your address book.
On the other hand, you can use concrete tags for specific tasks. For example, you can tag stuff (people, organizations, events and documents) related to a marketing campaign with a concrete tag 'Summer marketing campaign 08'.