Not a dumb question.. I had to look this up, too, once I started ttc.
So your ovulation day, the egg busts out of the ovary, right. The end of the fallopian tube is sorta attached near the end of the ovary, and does these rhythmic contractions that pull the egg down into it. They are also lined with cilia (little fingerlike protrusions) that "wave" with the motion of the tube, and propel the egg down into the uterus.
THAT being said, it takes something like 5 days for the egg to journey down the tube, and another one or two to implant. That's why if you look at charts that show an "implantation dip", that dip usually occurs between 7 (fast egg) to 10 (slow egg) days post-O. The dip is caused by a brief estrogen surge that results from the egg implanting. It is also partially caused by the slow decrease in progesterone (makes your temps rise), as the corpus luteum (leftover egg follicle) stops producing it somewhere around the end of your luteal phase. Your temps stay high with a conception cycle because the implanted embryo starts producing its own progesterone and eventually hCG.
*whew*
Also: I enjoy that I am the bitchy devil smiley
EDIT: sorry, I forgot the second part of your question. The egg only has about 24 hours to get fertilized, or else it kind of dies. So, you can BD up until 1 or 2 days post-O, but after that you're pretty much out of luck. Even if the egg makes its way to your uterus, and there's sperm there, it needs to be fertilized right when it pops out or no dice. Similarly, there's not much you can do to "encourage" a fertilized egg to implant. Sometimes, it implants in a less than optimal spot (in the tube, on your cervix, etc) and that usually leads to a miscarriage. Nothing at all you do can influence that. So yeah, if you BD after 2dpo, it's usually just for fun at that point.