"Paying quarterly taxes" can be confusing since you only file one income tax per year ... what it is referring to is paying in quarterly ESTIMATED tax payments so you can avoid an underpayment penalty.  When you are a waged employee the taxes are withheld from each paycheck  ... when you are self employed you pay them yourself on a quarterly basis.

What are estimated taxes?

https://ttlc.intuit.com/replies/3301588

Do I need to make estimated tax payments to the IRS?

PAYING ESTIMATES
For SE self employment tax - if you have a net profit (after expenses) of $400 or more you will pay 15.3% for 2015  SE Tax on 92.35% of your net profit in addition to your regular income tax on it. So if you have other income like W2 income your extra business income might put you into a higher tax bracket.

You must make quarterly estimated tax payments for the current tax year (or next year) if both of the following apply:
- 1. You expect to owe at least $1,000 in tax for the current tax year, after subtracting your withholding and credits. 
 
- 2. You expect your withholding and credits to be less than the smaller of: 
    90% of the tax to be shown on your current year’s tax return, or 
  100% of the tax shown on your prior year’s tax return. (Your prior year tax return must cover all 12 months.)

https://ttlc.intuit.com/replies/3301891

How do I make estimated tax payments?

https://ttlc.intuit.com/replies/3301258

Can TurboTax calculate next year's federal estimated taxes?

https://ttlc.intuit.com/replies/4242911

Can TurboTax calculate the estimated payments for next year's state taxes?

https://ttlc.intuit.com/replies/3301735