You have read about El Niño and La Niña in the weather section: basics - Circulation Systems - El Nino
and in more - Major wind systems - El Nino & SOI
You also should have had a look at the Worksheets 3, 4 & 5 in weather - basics - Circulation Systems on El Nino.
Now let's have a look at La Niña:
El Niño is world famous, not so the other extreme of the oscillation:
La Niña who brings colder sea surface temperatures.
And the third phase of ENSO is neither La Niña nor El Niño, just normal average.
Do you remember the facts (years 1950 to 1997)?