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You'll notice black wires around the joints of character models, at the base of the model, and as control panels above the character model.  Click this wireframe to select it.  The entire wireframe should turn orange. In 3D animation, armatures go inside a character model and act as bones and joints. They keep all the parts of the character attached and allow you to move parts of the model. Object mode is the default mode in Blender 3D.  Once you select the armature control rig, click the drop-down menu that says "Object Mode" in the upper-left corner of the 3D view, then select Pose Mode to switch. If Pose Mode is not available in the drop-down menu, you do not have a valid armature rig selected. The black lines around the model are generally moveable parts of the right.  Click one of the moveable parts.  It should turn blue. To move a part of a character model in Pose mode, click the black line around a joint on the model, or one of the sliders in the control panel above the rig, and then press G to grab the part. Drag the mouse to move it. These Minecraft rigs have many unique animations already programmed in. You can access these animations using the control panel above the rig in Pose mode.  Experiment and see what kind of poses you can get from the rigs.
Click the armature controls of a rig. Switch to Pose mode. Click a moveable part of the rig. Press G to grab and move the part.