The JSTL Core library for JSP provides features like iteration over a collection and testing conditions. Iteration is handled by tags such as <c:forEach> and <c:forTokens>, while testing conditions is enabled by tags such as <c:if> and <c:choose>. Message localization, while important, is typically managed by the JSTL Formatting library, and buffering of large result sets is not a primary feature of the JSTL Core library.