An impulse response (IR, for short) is a sound measurement that takes into account the conditions around a guitar cabinet speaker, including the room, microphone and mic preamp. This information is stored in a .wav file to be loaded into a convolution plug-in.
An impulse response does NOT include the tonal characteristics of an amp head, which means gain & effects need to be applied using other tools. As far as the end-user (you & I) should be concerned, IRs should be replacing the cabinet in a traditional, live guitar setup.
Because impulse responses are stored as .wav files, they are universally compatible, relying on your computer and software for the heavy lifting.
See our guide for Getting Started with Impulse Responses here - https://joeysturgistones.com/blogs/learn/getting-started-with-impulse-responses-for-guitar