not sure what previous posts and confusion is
your tax is calculated progressively up these bands so you pay 10% tax on the first 11.6k of taxable income, then you pay 12% on whatever income is above 11.6k until 47k, then you pay 22% on any income above 47k to 100k etc.
if you have long term cap gains or qualified dividends those will get a different tax rate which is stripped out first. See the "Qualified Dividends and Capital Gain Tax Worksheet" which does that math and then the residual taxable income which will go through the tax tables/calculation worksheet using these bands. There may be other taxes/worksheets that drive your final tax liability, see Form 1040 line 16 onwards.
See the IRS tax tables for the calculations https://www.irs.gov/pub/irs-pdf/i1040tt.pdf
Your effective tax rate is an 'average' rate which is the result of all these different tax calculations and rates for different layers of your income; this would likely be lower than the highest bracket you hit during this process.
When thinking about what "tax bracket I am in" I suppose it's most helpful to know the highest bracket your income hits during the process and therefore the tax rate that would apply to any additional income.
