Surge has a cool set of effects, and also works as an audio input source in most DAWs so you can use them using routing and latch mode with the full synth.
But in a couple of situations, it is powerful to have the surge effects as a separate plugin. The Surge Effects allow you to do this. The Surge Effects plugin is included as an extra plugin in the mac and Windows surge installers.
To use Surge Effects, simply drop the VST3 or AU into your DAW as a plugin in an effects slot. The controls are fairly obvious, but the knbos adjust levels and the switches allow tempo-sync for controls where that is appropriate.
The one feature Surge Effects offers which is impossible to do in Surge proper invovles the Vocoder. The Surge vocoder is a powerful tool in Surge, where the sidechain acts as the modulator and Surge itself acts as the carrier. But using the Surge vocoder with a sound source other than surge as a carrier requires two sidechains, a feature which is unsupported in modern DAWs. With the Surge Effects plugin, you can sidechain a modulator in but use the current track for a carrier source, allowing other synths or audio sources to provide carriers into the vocoder circuit.