Minnesota -420
San Francisco +330

You could bet $100 on San Francisco to win and the payout would be $330.

OR

You could bet $420 on Minnesota to win and the payout would be $100.

I think handicapper's use $100 because it looks like a more profitable bet on paper. But you can use $10 too.

You could bet $10 on San Francisco to win and the payout would be $33.

OR

You could bet $42 on Minnesota to win and the payout would be $10.

The strategy is to try and find the best moneyline for the week based on the match-ups. I'll use Minnesota, again, for an example. When they played San Diego about 4 weeks ago the Chargers were heavily favored; the moneyline was something like:

Minnesota +800
San Diego -1300

A $10 bet could've won $80. Not bad!
References :
http://www.betus.com/sportsbook/straight.aspx

It lists the two teams, the opening point spread, and the current point spreads and over / unders from each of four different sports betting sites.

The + and - (point spreads) correspond to the SECOND team listed immediately above. For example:

NEW ORLEANS @ ATLANTA
open: +4.5 42.0 O/U
BetUS - Sportsbetting - Sporsbook - BoDogLife
current ….. current ……… current …… current
. 43.0 ……… 42.5 …………. 42.5 ………. 43.0
. +3.0 …….. +3.5 …………. +3.5 ………. +4.5

Here Atlanta (the second team listed) is "getting" (plus) points. Basically you're adding (therefore the plus sign) anywhere from 3 to 4.5 (depending on which site you place your wager) points to Atlanta's final actual score to arrive at the adjusted score for the purpose of betting. So if New Orleans wins the game 30 to 28, Atlanta, even though they lost the game, would win the bet because the "adjusted" score would be 30 (New Orleans) to 31-32.5 (Atlanta), depending on which site you chose to place your bet with.

Frankly it's kind of odd to see such a large margin between odds on the different sites, especially this late in the week, but that just proves why it's important to "shop around" and look for the best deal. If you had a hankering to place a wager on New Orleans, you'd obviously want to place that wager on BetUS since you'd only be spotting 3 points to the opponent, however if you wanted to bet on Atlanta, you'd opt for BoDogLife since they're spotting them 4.5 points!

Don't concern yourself too much with the "open" number, as you're betting based on the current (today's) point spread, not what the point spread was at the beginning of the week. And lastly, the other numbers are the "totals," or "over / unders" for the game. In the above example, if you think the combined total of New Orleans' AND Atlanta's scores will exceed 42.5 or 43, you'd bet "over," otherwise you'd bet "under."
References :

Those are two separate bets.

NFL is not usually bet straight up (with odds), you'll have to look deeper into one of the sports books to find the odds.
References :