No, it's not that, but I think I might know what you're confused by.
What is the source of surplus value (where does profit comes from)?
Marx says it's labour, specifically the value of a commodity is determined by the labour time socially necessary for its production. (in other words the average, if one capitalists factory isn't very efficient and the production of commodities takes longer, it doesn't mean that those commodities will be worth more, obviously. Because when they're sold on the market they'll be undercut by the competition. They'll only get as much as the average "value" .)
Your wages for your working day don't correspond to the whole value of what you produce. This is obvious - if they did they'd be no profit for the owner of the firm, or more likely, shareholders. Shareholders do no work for the "investment income" they receive.
But this isn't really a matter of value being stolen. Because really you're not being paid for your labour time. I know this may sound weird! As your wages will probably come in the form of pay per hour. But as we've seen, your labour time produces more value than you are paid for. It's more like sleight of hand trickery than value being stolen. Because what your are being paid for is your "labour power" - this is basically your living expenses, rent, food, entertainment, etc. It's basically everything that you need to keep you going. You could say its like the money the capitalist has to pay out to keep his machines oiled and maintained. The only difference is the machines in a factory or wherever don't create surplus value.
Hope this makes sense. I'm typing it 6.30 in the morning before I've had any coffee. Woke up needing to use the toilet, thought ill just see what depravity is going on on /leftypol/.
Please feel free to ask anything if what I've written isn't clear.