# How to read nash equilibrium from a normal form?

For example, on the section with the title "sequential games in normal form" of this wikipedia page, there is a table with all its SPNE and nash equilibrium labelled. How are the NEs obtained? It seems have something to do with the underlined numbers in the table. However, I am not sure based on what rule are the numbers underlined.

Assume the second player plays (K,K), then which one you are going to play? L or R? Of course - L (as $$3>2$$). Then assume the second player plays (K,U), what is the first player's best strategy? It is again L (because $$3>0$$). And so on.