Red clover is no different from any other clover except that it has pretty little red blooms. Like all clover, it contains coumarin, which is the active ingredient in most rat poisons. Yes, rat poisons. It makes the blood "thin," so to speak. Specifically, it blocks some clotting factors so that the blood does not clot as quickly, and when eaten in large quantities, it can bring down a cow.
I start with that caveat because some folks just go overboard with herbs. More is better! Not so.
Like soy, red clover has isoflavones. However, it contains far more isoflavones than soy. Isoflavones are hormone-like substances that are similar enough in shape to bind weakly to some hormone receptors. That's very useful for women in menopause who have fluctuating levels of hormones, and it is debatable if it is helpful or harmful for those with excess estrogen, like women with endometriosis or fibroids. Theoretically, if you can block some of the real estrogen from its receptors with something that is weaker, the action of estrogen would be decreased.
Aside from the isoflavones, red clover has many other vitamins, such as magnesium, calcium, potassium, B vitamins, and vitamin C. Some people eat it on salads as it is very sweet.
It is used for eczema and even cancers, probably due to the isoflavone content.
Red clover is claimed by some herbalists to help with infertility. Generally, it is ingested as a tea, but I have also seen supplements. Probably the tea would be more potent, as most teas are. Also, you can't confirm how much is actually in a supplement.
I have found red clover touted as good for infertility, but I am not sure why unless it is due to the B vitamins. I have written before about the benefits of B6, and that would certainly be helpful. The isoflavones in red clover would not be helpful for fertility, however, and they may even decrease fertility. If you have PCOS or fibroids, both of which are linked to excess estrogen, taking red clover for a while before you try to conceive might help decrease your estrogen receptor sensitivity, which would be good. But if you are actively trying to conceive and think that red clover will help, I doubt it will.