Connection between genes and pathways
ERBB2 appears to be a (tyrosine kinase) receptor; that is, it lives in the cell membrane; with a part that sticks outside of the cell, and part that sits inside.  When the right molecule attaches to the outside part, the inside part changes shape, which alters its function, causing it to start phosphorylating other proteins, which alters their functions.

So the ERBB2 pathway is the set of genes/proteins whose behavior is affected by ERBB2.

Google "ERBB2 pathway" and "tyrosine kinase receptor" for more info.