In the standard model, every Feynman diagram is constructed using a combination of specific vertices. Here, q represents any quark, g stands for a gluon, X denotes any charged particle, γ symbolizes a photon, f signifies any fermion, m refers to any particle that has mass (except potentially neutrinos), and so on. When a diagram features multiple particle labels divided by a "/", one of these labels is selected. Conversely, if the particle labels are separated by a "|", they must be chosen in sequential order.
It was in 1948, at the Pocono Conference where Richard Feynman first introduced these diagrams. In the spring of 1949, he published a paper explaining the Feynman diagrams. Here's an interesting article to understand these diagrams in laymen terms:
https://piggsboson.medium.com/feynman-diagrams-for-laymen-d0a27fb415b8
