Not all golf courses require that golfers reserve a tee time, but many do. Still others don't use tee times at all. So any time you want to play a golf course you've never visited before, it's prudent to call well in advance and inquire about its tee time policy.
What's the purpose of a tee time? To help organize golfers on the course, and to try to maintain a good flow of golfers around the course. Tee times are spaced at regular intervals - typically from seven to 15 minutes apart, depending on a given golf course's policy - so that groups of golfers are beginning their rounds in an organized fashion.
The most common practice is for golf courses to accept tee time reservations several days in advance, but that policy, too, is set locally. Those public courses golfers are most desirous of playing - Pebble Beach, for example - might accept tee times a year in advance. Again, when you're unsure of a course's tee time policy, call well in advance (or visit the course's Web site).
It's possible with some golf courses to reserve a tee time online, via the course's Web site or through a third-party Web site (a tee time reservation service).
Tee Time FAQs
For more info about tee times, see these FAQs:
Are tee times required to play golf?
How do I get a tee time?
Are tee times available online?
If I show up at a course without a tee time, will I get to play?
What happens if I'm late and miss my tee time?
"Hello, I'd like to get a tee time for Tuesday, somewhere in the 10 a.m. neighborhood."