Download the R15IK Blender archive and open it, you will see a Roblox Rig and a bunch of others things. Must be something like this Now, let's see how to animate with the Rig.

An R15 humanoid character model, such as those that make up user avatar characters, is made up of 15 individual mesh objects. Similar to rigging a simple mesh, you can bind or parent a group of meshes ...