How do I use the third symbol on the key underneath the Esc key on a keyboard? I know how to use ¬ and ` but not the third (a vertical line)

Usually a third symbol on a key will require the holding of another key to apply that symbol as when holding the shift key to go upper case and what not. But the third the symbol is usually a different color and the key to press to access that symbol is the same color as the symbol is. Such as with many laptop keyboards the FN key (usually at the bottom left side of the keyboard) is a bluish color and pressing it is required to apply the blueish symbols on keys.
I hope this helps.