When a woman has a discharge, [it can consist] of [any] blood that emerges from her womb. For seven days she is then [ritually unclean] because of her menstruation, and anyone touching her shall be unclean until evening...Vayikra (Leviticus) 15:19
If a woman has a discarge of blood for a number of days when it is not time for her menstrual period, or if she has
such a discharge right after her period, then as long as she has this discharge she is unclean, just as she is when
she has her period... Vayikra (Leviticus) 15:25
When [the woman] is rid of her discharge, she must count seven days for herself, and only then can she undergo
purification (by immersing her body in a mikvah)... Vayikra (Leviticus) 15:28
The sources in the Torah that deal with this is Vayikra 15:19-32, the Mishna in Tractate Niddah, the Talmud in Tractates Niddah, and scattered through various parts of Tractates Shabbat and Shevuot.
In the Shulchan Aruch, this issue is dealt with in Yoreh De'ah, Simanim (Chapters) 153-200.
However, there is no substitute for a one on one with a teacher experienced in this subject that can help guide a young couple to make sure that these beautiful laws result in the marital harmony that they are meant to achieve, and not cause problems, which improper understanding of these laws can easily bring.
The following is a quick summary of the various stages of the laws involved: