A separate reply to the buying terms you asked about.
A "market order" is an order that says you'll just pay whatever the seller is asking for. Kinda like going to the store and just buying stuff --- you don't dicker for the price -- you just pay whatever the seller wants. MOST people use a market order... because unless you're buying lots and lots of shares -- it really doesn't make much difference if you pay a penny or two "more or less".
A "limit order" is what I prefer to use. I buy shares 5,000 or 10,000 or 20,000 at a time. A few pennies on orders like this adds up. So ------ when you place an order -- the question will come up (in a box) what type of order you want to place. If you place a LIMIT ORDER then you must fill in the MAXIUM price you are willing to pay per share. You can match to current ask -- or you might chose to "bid" a penny or 2 -- or even 10 cents less!
Now -- you can modify your limit order with "good for day" or "fill or kill".... so if you use good for day then your bid is "open" until the market closes.... and you might sit all day -- and then 10 seconds left in the trading session and some seller decides he's going to accept your offer and fill your order (maybe only partly or in whole).
The FILL OR KILL --- means you have a very short fuse and are willing to only accept a FULL order fulfillment and it must be filled RIGHT NOW no waiting for the end of the day crap.... and if not - you want the order killed.
The above is very basic..... so if you really want to dig into the nuances of trading (I do not recommend trading -- I like to INVEST).... you can find good detailed answers to just about any market info here:
http://www.investopedia.com