Sorry, I'm not familiar with that feature in Flash and a quick search doesn't turn up much.
Pose tool docs are here:
Tools - Spine User Guide: Pose tool
To use IK with the Pose tool, select 2 or more bones then start a drag from any of those bones (or the handle at the tip). You can give that a try in the Spine trial.
The Pose tool is sort of Spine's "multi-tool". It can do both rotation and translation, without you needing to change tools. To translate, drag from the origin (start) of a bone. To rotate, drag from a selected bone or the handle at the tip of a selected bone.
Unlike all other tools in Spine, the Pose tool is the only one that requires you to grab little handles to manipulate things. With other tools you can drag anywhere to manipulate the selected objects.