Our decimal number system uses positional notation, and so does binary, octal, hexadecimal etc.
Each digit gets multiplied by its place value. The place value is "base" times bigger for each position going left.
For "base 10" (the decimal number system):
• For 327 the 3 contributes 3×10×10, the 2 contributes 2×10, the 7 contributes 7
In "base 8" (the octal number system):
• For 327 the 3 contributes 3×8×8, the 2 contributes 2×8, the 7 contributes 7
(Note: by contrast Roman Numerals do not use positional notation: X always means 10, or minus 10 when in front of a bigger digit.)