Lo - In front, or behind?

Lo - In front, or behind?

I'm confused as to when to use "lo" or "le" in front or behind words?

For example:

No lo sé
Encantada conocerlo
La médica le responde - could you say "La médica respondele"?

How do I know which is correct? Are both correct and I'm just being shown different ways to do it?

Thanks,
Brenda

Lo is a direct object pronoun.
Le is an indirect object pronoun.
Does that make things as clear as mud?

The pronouns se, le, lo, la etc (1) must go before conjugated verbs, except in the imperative mood. (2) In the imperative (commands), the pronoun goes at the end of the verb, and they become one word (often necessitating a written accent mark BTW). (3) The pronouns may also go at the end of an infinitive or the present progressive participle. This is optional-- they can also go before the conjugated verb (main verb) of the sentence.

Me gustaría saberlo. (I would like to know [about it])
Dámelo (give it to me)
¿Me lo puedes dar? (Can you give it to me?)
¿Puedes dármelo? (Can you give it to me?)
Hágalo. (do it)
Házlo. (do it)