Question about quotations?

[Mnkys njoy nanas!]

Okay, so I'm writing this thing for fun, and this has started to bug me. Just a few questions.
a) If I'm saying something like: This is a "world."
Would I use the two quotation thing, or the apostrophe (This is a 'world.')? I've seen both.
b) In the above sentence, would the period go in front of or behind the quotation?
c) When doing dialouge, I know you must begin a new line for each person talking. Do you have to put an indentation there?
d) For the heck of it, what is the latest thing you've read or written?

[ro_c]

I've always used ["..."] as to mean someone saying something, and ['...'] as to mean a thought, concept or idea.

See: http://owl.english.purdue.edu/handouts/grammar/g_quote.html
or
http://grammar.ccc.commnet.edu/GRAMMAR/marks/quotation.htm

The last thing i've written is this

[yads]

a. either {note: 'one' quotations are also used when quoting a word/words inside a sentence/fragment enclosed in "two quotes"}
b. before the close quotation
c. it would look better if you did (easy to read and flow/picture of story becomes more vivid)
d. the latest i've written is this, this is also the latest i've read

[Pat K]

A. Two quotation marks

B. The period goes before the second quote mark.

C. No, you can just hit the enter bar and leave a full space between the quotes for each person, or use the indentation, or both.

D. Well, to be a bit humorous, the latest think that I read was your question, and the latest thing that I wrote was this answer. Otherwise, the latest read was the newspaper.