Hi there haikyufan123, and welcome to Scarleteen!
A period is the result of a monthly cycle in which the body normally prepares to ovulate, ovulates, and then sheds the uterine lining if pregnancy does not occur. Periods often happen on a regular cycle (26-32 days, depending on the person), but they can be influenced by stress, medications, and changes in diet. If someone is taking a hormonal form of birth control, periods and their side effects tend to be a bit lighter and a bit more predictable.
A miscarriage happens when someone has been pregnant, and then the contents of the womb are expelled via cramps, either spontaneously, as the result of being hurt or unwell, or intentionally via an abortion method. There may be fluid, clots, or tissue, depending on what that stage of pregnancy that person was at and their health. Symptoms that can accompany a miscarriage are like those of period, but usually more intense.
You can read more about periods over at On the Rag: A Guide to Menstruation
, and miscarriages over at Miscarriage: What It Is, How It Happens, and How To Deal
Is that the type of info you were looking for?