If you're new to Sports Betting, which it sounds like you are, you really should take the time and read the forum FAQ:
A line that is -110 means you must lay 110 to win 100.
A line that is for example -115 means you must lay 115 to win 100.
You can obviously do the very easy math to scale that to your accurate units, for example two units at -110 if you're betting $20 per game would be $44 risked to win $20.
If you can't do this math for some reason, you can use an online calculator, for example:
http://www.smartcapper.com/tool_payout_calculator.html
Most people track units as "to win" for negative lines and "to risk" for positive lines",
i.e. a listed bet of "two units on Philly -3 -110" (for $100 units) would be $220 risked to win $200, but a bet of "one unit on Dallas +7 +105" would be $100 to win $105.
-P