Which structures form gynoecium? How is placenta related to gynoecium?

Which structures form gynoecium? How is placenta related to gynoecium? What are its types?

Gjnoecium is the female reproductive whorl of the flower. It is composed of one or more carpels. Each carpel is differentiated into three parts, i.e., the ovary, style and stigma.
Placenta is the tissue on which ovule (s) develops in the ovary. The placentation in the ovary may be
(i) marginal (ii) axile (iit) parietal
(iv) basal (v) free-central