Here's how the normal female feedback loop works.

At the end of your cycle, your P4 levels drop off and when it's low enough, your menses starts. In addition, the low P4 level signals your pituitary gland to start producing FSH. The FSH is used by the ovaries to start developing follicles. As the follicles grow, they secrete E2 which signals the pituitary to reduce the production of FSH.

A diagnosis of High FSH indicates that the body is not processing the FSH secretions properly.  In my humble opinion, this can be due to a number of reasons:

(a)  the pituitary gland is not getting the right signals from the elevated E2 levels (caused by the growing follicles)

(b)  the pituitary gland is getting the right signals but is not processing them properly

(c)  the growing follicles are not secreting enough E2 to signal the pituitary glad to reduce FSH production.

In the case of (a) and (b), it seems that a pregnancy should be possible.  However, in the case of (c), it seems that if the follicles aren't growing and maturing properly to give off enough E2, then pregnancy would be harder to achieve.  It also seems to me that many doctors think along the lines of (c) - High FSH means poor egg quality.  I for one don't completely buy into this.

Moving on, as the follicle(s) mature, they continue to release increasing amounts of E2.  When your E2 level gets high enough (around 1000+ but everyone is different), it signals the pituitary gland to release a sudden and extended surge of LH. The surge lasts ~36+ hours. At the peak of the LH surge (~36 hours), ovulation occurs (this timing is pretty consistent, +/- a couple of hours, for all women). After ovulation occurs, the follicle that released an egg (and any other follicles that developed but didn't ovulate) start to breakdown into a corpus luteum.

Note:  When using an Ovulation Predictor Kit (OPK), the LH surge is detected as long as 4 hours after it starts.  If you are monitoring with OPKs, you can monitor multiple times during the day.  I caught my first surge at 10:00pm after my 7:00am and 2:00pm OPKs showed nothing.  This can be critical for some women who want to zero in on when they'll ovulate. 

The corpus luteum(s) of both the ovulated follicle and any smaller follicles that did not ovulate secrete P4 which is necessary to develop the uterine lining in anticipation of supporting a fertilized egg.  The better the quality of the follicles (and therefore the eggs inside), the higher the P4 level and the better prognosis for developing a good lining.  Women who go through IVF and routinely put on P4 supplements since IVF can remove the corpus luteums and therefore remove the P4 supply needed. 

Note:  As an aside, one of the side effects of elevated P4 levels is constipation.  P4 acts to relax or slow down some muscles.  As a result, the intestines move slower and ... constipation.  In addition, the sphincter muscle at the bottom of the esophagus can also relax causing acid reflux (not pleasant).  As many women will tell, Metamucil and Tums will become your best friends.  It is recommended to start an anti-constipation regime before the slowdown hits and to keep a bottle of Tums handy at all times.

About 5-7 days after ovulation, and with a bit of luck, a good fertilized egg implants into the lining.  A fertilized egg can also implant late so figure up to 10 days after ovulation.  Once the egg implants, it starts to secrete HCG (actually it starts to secrete HCG when it's fertilized) to help sustain the lining during the first 9-12 weeks.  It is elevated HCG that Home Pregnancy Tests (HPTs) test for.

However, if there is no fertilized egg, or it is not a good enough quality to implant, the P4 level starts to drop off as the corpus luteum secretions dry up. Once the P4 level gets low enough, menses arrives and the cycle starts all over again.

That's it in a nutshell.

Glossary

P4 = Progesterone
LH = Lutenizing Hormone
FSH = Follicle Stimulating Hormone
E2 = Estradiol/Estrogen
HCG = Human Menopausal Gonadotropin