I'm trying to make almost the same exact stairs as seen in Verruckt, however I can't find where the Vertex Editing functionality is in Radiant. I'm pretty sure Radiant would have the functionality.

Try pressing the "E" key to bring up edges editing and "V" for vertex editing. Do this while you have a brush or patch selected, then drag the squares around by selecting them and then dragging with mouse. Hold shift and drag to select multiple vertices.