Let's say you have $50,000 in TAXABLE income so you owe say $5,000 in income tax (Federal, making up figures). If you get a tax credit of $1,000, you will only ow $4,000 in taxes.
If you get a tax deduction of $1,000, you now owe tax on $49,000 of income, or $4,900.
Tax CREDITS are comparatively rare things, you might get one for buying an electric car for example. Tax deductions are dime a dozen today.