The last post on Spanish for the Professions was all about professional introductions. It concluded with an admonition not to confuse the Spanish verb for introducing people (presentar) with the verb for inserting coins or credit cards into machines (introducir).
A similar confusion arises around the past tense of the verb conocer.
In the preterite, it means "met" (as in, to know for the first time):
-Conocí a mi esposo en California hace 15 años.
(I met my husband in California 15 years ago.)
In the imperfect, it means "knew" (as in, I used to know):
-Conocía a Jeff cuando era niño, pero no lo he visto desde hace mucho tiempo.
(I knew Jeff when he was a boy, but I haven't seen him in a long time.)
This is one preterite/imperfect difference that is clear cut. Enjoy it!