Those links outline how it is calculated, but here is another way to phrase it:
Let's say you bought the home for $200,000, took depreciation of $100,000, and sold it for $500,000.
If you sell it in summer of 2021, you will have a gain of $400,000. Of that, $100,000 (from depreciation) will be tax at your regular tax rate, and $300,000 will be taxed at the long-term capital gains rate.
If you make it your Principal Residence for two years, this is how it would work: You would have about 12.5 years of "Nonqualified Use" (rental after January 1st, 2009) which means you have 13.5 'qualified' years out of a total ownership of about 26 years.
If you do that, you would still have the $100,000 from depreciation that will be taxable at your regular tax rate. But the other $300,000 will be prorated. You can "exclude" (not pay tax on) 13.5/26ths of the $300,000. So rather than having $300,000 of long-term capital gains, you would only have $145,000-ish of long-term capital gains.
Again, you would need to make it your "Principal Residence" for at least 2 years to do that.
Things are a bit more complicated than that, but that should give you an idea for what the difference would be.
