w3schools, I find, is great for quick reference to the details, but not strong on teaching the underlying concepts. There are three things you need to know here:
(a) xsl:for-each establishes a current node. Within the for-each, you will normally make selections relative to the current node. You can refer to the current node as ".", so for example <xsl:value-of select="."/> gives you the string value of the current node.
(b) a path expression starting with "/" selects from the root of the document. Using it inside a for-each will therefore give you the same selection each time.
(c) In XSLT 1.0, if <xsl:value-of select=..."/> selects multiple nodes, then only the first one is displayed. That's "Accounting" in your case.
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference