as rumpelstiltskin said, segulos should not take the place of Tefillah and Tshuva.
But there is a spiritual, non-physical world in which we live along with the visible physical one. it has properties and “laws” just like the physical one. (explained well in the Ramchal’s “Derech Hashem”) we dont see it consciously but the Chochomim do. much of the segulos come from practices they did in concordance with that knowledge. this is the root of the idea of segulos. but were all mixed up today and often cant tell a segula founded in reality from one that may not be.