So many questions... =)

[BeckyDi]

I've been going through the Rosetta Stone program for a few months now, most of the material had been review from high school but I've run across a few snags just this week and I'd be SO grateful for any help you guys and gals can offer!

Question #1
"Debajo de la mesa" and "Debajo la mesa" both mean underneath the table - so why the "de la" and "la"? Are there appropriate times to use one or the other? And why when you say "on the table", it's always just "sobre la mesa" with no "de la"?

Question #2
When you say "Yo quiero a mi esposo", it means "I love my husband", right? But when you leave out the "a", so "Yo quiero mi esposo", does it mean "I want my husband"?

Question #3
I've seen both "Encantado de conocerte" and "Encatado de conocerlo". Translated, these are both "Delighted to meet you", but why does one end in "te" and the other ends in "lo"? I always thought you attached "lo" when talking about something you were referring to as "it".

Question #4
I've seen both "?Como se llama usted?" and "?Como te llamas?" (both said to a single person) and when translated, both mean "As you are called?". Are these used interchangeably or is there a proper place/time to use one or the other?

Question #5
What is the difference between "es" ("it is") and "está" ("it is")?

Question #6
When do you use "tú" and "usted"? I always thought "tú" was used when you were speaking to someone younger than you and "usted" was used when you were speaking to someone with respect, as in someone older than you.

I apologize for coming in and immediately dropping this help bomb of questions - I hope I'll be able to offer some help to others eventually! Thanks in advance for your help! =)