@StarPlatinumTheWorld The well known decimal system uses ten symbols to identify quantities from 0 to 9. After 9, if you add anothe unit, the counting identifies that one set of ten is complete, and that there are no new units for a new set, therefore the numer 10 follows the number 9.
In the octal system, the symbols available are only 8, and they go from 0 to 7. When you add an additional unit to 7, one set of 8 elements is complete, and there are no new units, therefore the number 10 in octal base follows the number 7.
It is possible to perform conversions from the octal base to the more common decimal base, as well as perform the reverse conversion, from the decimal base to the octal base. These conversions require the use on multiplications or divisions, depending on the direction the conversion.
However, some notable numbers in octal base can be easily converted: for example 10 in base 8 corresponds to the number 8 in base 10. Also number 100 in base 8 corresponds to 8*8 = 64 in decimal base.
Do I need to go on for much longer, or did I cover enough for 3 minutes? Other topics you could add are the conversion to/from decimal base, and to/from binary base which makes a mathematically interesting point, and 3 bits grouped together can be converted to an octal number...