After a rig has been tagged, you can load and apply retargeted mocap data to it. Mocap data that's already been retargeted (normalized) is saved in the .motor format (see Saving Animation Data in Normalized Motion (.motor) Files).
You can retarget and save .motor files from C3D mocap data or from BVH mocap data (see Retargeting Mocap Data from C3D or BVH Files to a Rig).
You can also animate a rig in any other way, such as with keyframes or action clips, and save that in a .motor file as well.
Retargeting and saving these types of data in files makes it easy to build up a library of animation files that can be applied to any tagged rig.
To apply a normalized motion file to a rig
Make sure that the rig has been tagged, as described in Tagging a Rig's Elements.
With the rig selected, choose Tools 
MOTOR Load Motion from the Animate toolbar.
In the Motor File property editor that appears, click the browser button (...) beside Motor File to go to the appropriate folder in the browser and select a .motor file.
Enter a Load Setting Start value, which is the frame at which you want to start the .motor file, then click the Apply button.
The animation from that file is applied "live" to the rig at the frame you specified.
If you want to adjust the normalized motion, click the Adjust button to adjust it as described in Adjusting the Retargeted Animation on a Rig.
To remove the normalized motion from the target rig, select it and click the Remove button.
If you want to apply the normalized motion as fcurves on the rig's parameters, click the Plot button to plot it as described in Plotting Retargeted Animation on the Rig.
You can also retarget the animation from this rig to another tagged rig, as described in Retargeting Animation from Rig to Rig.