Online sales and quarterly tax payments

Please excuse my ignorance. As a single member LLC, when it comes to making sales online and making quarterly tax payments to the IRS, am I supposed to pay 20% of income from my sales?

For example (imaginary #s), I buy a product from my distributor for $50, and then sell it for $100; do I just set aside $10 (20%) from each sale in order to mail a check to the IRS each quarter?

Thanks for any help.