What's a "brick" and why is it named so?
For us beginners, a brick is usually a bike/run combo. This simulates the bike to run transition - many think is the toughest part of the race. It should be done during your final training phase leading up to a race. A brick simulates the bike-to-run transition. It's wiggy. Have you ever had your leg go to sleep on you? You can move it ok but you don't feel like it's part of you. Really. It's like running on rubber pegs or running with a ball and chain attached to them.
Bricks are usually demanding on your body - don't make them routine. Definitely plan on doing 2-3 bricks during your final lead-up to your triathlon. When doing these bricks, you don't have to run your best time - go easy. I wouldn't even do your full miles. What might also work during your last several weeks to a month is to maybe do an easy mile of running after every bike ride.
Also, at the end of the bike leg, lower your gear and increase your pedal revolutions to loosen muscles tightened by pushing big gears.
If time is not a bother to you, it will definitely NOT hurt to take a few minutes to stretch those leg muscles.
But finally, the truth is that the 'bricks' I have been talking about are...well...whimpy. If your a serious triathlete, a true brick is to do several bike/run combos. Ughhhh!!!! Good thing we don't have to worry about that for now.