bb in short......think of it like this:
if you make $100k (net) as a sole prop (or LLC taxed as a sole prop), then the entire $100k is subject to SE tax (equivalent of payroll taxes)....there are rough calcs, but it is basically 15.3% of your first $100k (limits change every year)....this is in ADDITION to the fact you have to add the $100k as income on your tax return.
If you have an S-Corp, you will HAVE to take salaries as a shareholder (and essentially pay the same 15.3% on that amount) but you do not have to take the entire $100k as salaries.....basically if you only take $50k as salary, the other $50k isn't subject to the SE tax.
(either way you are reporting $100k on your individual tax, just in option 2, 50k is W-2 and 50k is via K-1)