Track workouts are generally a more-structured type of speed workout that usually consist of some sort of intervals–a period of hard running with a period of easier running and/or rest, then usually repeated several times. Again, the distance and speed of your intervals depend on both the type of race you may be preparing for and also your current fitness level.
For a 5k or 10k, I like to do 400 meter (quarter mile/1-lap on most outdoor tracks) repeats. I do a fast 400 followed by either a 200 or 400 meter rest jog, then repeat. I find it helpful to have my interval and my rest period times planned out ahead of time. For example, the 400 repeats with a 1:45 goal with a rest of 2:30. This means I’d run my fast lap in about 1:45, then immediately go into a very slow 200 meter jog, and once it’s complete just rest for the remainder of the 2:30 rest (stretch, hydrate, finish catching your breath, etc). As soon as the rest period is up, go right into another fast interval. Start with 4 or 6 if you’ve never done this type of workout and add more intervals and adjust pace as you become comfortable.
For a half marathon or marathon, I like half mile and mile repeats, set up similarly as shorter intervals.
You may also find what’s called a “ladder” workout fun and effective: start with shorter intervals and gradually make them longer, and even work your way down. For example, run a 200 meter (1/8 mile), 400, 800, mile, 800, 400, and finish with another 200, all with appropriate rests in between.
Another idea is to base your workout on heart rate (for those of you with a heart rate monitoring device). Run your fast intervals with the goal of reaching/maintaining a certain heart rate, and then your rest period would extend until your heart rate has fallen back below a certain mark. For example, I might do my 400s with a goal of reaching an heart rate of 175, and then my rest would go until I dropped back below 120.
The last strategy can be done without a heart rate monitor, of course. Simply do your intervals at a hard pace that is maintainable (and repeatable!) and rest until your pulse and heart rate have returned close to normal.
As much as I enjoy being outside, this workout can be pretty easily mimicked on a treadmill as well.