INSTALLATION
-click green "<> Code" button from the top of this page
-in pop-up menu click "Download ZIP"
-run Blender. Go to Edit -> Preferences -> Add-ons
-click "Install" button
-choose geo_nodes_primitives-main.zip from the folder where you downloaded it
-click "Install Add-on" button
-activate the addon by clicking the square next to its name
USING
-in 3d Viewport go to "Add" -> "Mesh"
-click "GeoNodes Cylinder"
-to change the parameters of the cylinder that you just made, go to Modifiers Properties (wrench icon) and tweak parameters of GeometryNodes modifier
Thanks to guys from blender.stackexchange.com for the parts of code (especially to https://blender.stackexchange.com/users/109459/x-y)
and to Sergey Turandin for testing