Algorithms are added to the graphical modeler in the same way as inputs. Find the algorithm from the Algorithms tab, and either double-click on it or drag it onto the modeler canvas. You can search for tools as you would in the Processing Toolbox. Type the name into the search box at the top of the Algorithms tab:
Here we see the Algorithms tab with
buffer being used as the search term.
In the Algorithms tab, there is a special category named Modeler-only tools. The three tools—Calculator, Raster layer bounds, and Vector layer bounds—do not appear in the Processing Toolbox. They are tools that only make sense when they ...