Yes, it is known as the "juice". And it is typically 10%.
So if you like the Vikings minus 11 points on Sunday and you want to bet $1 on them, if you win, you will win back $.90 ($1.00 X .9) plus your original dollar so you will get back $1.90.
This is how the house makes their money. They try to get an even number of bettors on both sides of the sporting event then they will take in more money than they pay out.
If you want to bet on the Vikings without giving a pointspread, then you will see a line such as -400. This means that you have to bet $1,000 to win $400. Or in your case $10 to win $4. You are betting on a team that is a big favorite and not giving any points so you have to lay more money and you win less but it is a safer bet.
Stick with small stakes, bet on more underdogs and you will get the hang of it soon. Good luck!