[header] How to swim underwater without holding your nose [title] Get into the water and stand by the edge of the pool. [substeps] Standing by the edge of the pool will ensure that you feel secure while you go through the following steps. It is a good idea to stand waist-or chest-deep in the pool, whichever you are more comfortable with. 
[title] Slowly dunk your head underwater while blowing air out through your nose. [step] Exhaling through your nose is the main way to be sure that water doesn't get into it.