False friends are words in two languages that look or sound similar, but differ significantly in meaning. An example is the English "embarrassed" and the Spanish "embarazada" (which means pregnant), or the word "sensible", which means "reasonable / razonable" and "sensitive" meaning "sensible" in Spanish...
Meanwhile a cognate is an easy word to remember because it looks and means the same thing as a word you already know. For example, "gratitude" in English means the same as "gratitud" in Spanish.
Here you have a list of the most common false friends: