How federal tax deduction work in BC,canada????

just wondering how this tax deduction work in BC, canada ..sometimes i look at my pay check i got more deductions and sometimes less .. and i am only concerned with federal taxes ..it might be possible that it varies with provinces too but i am not sure about that..so could anybody can explain me this thing ..do they cut taxes as some %age of gross income ??? do they have some different criteria for part time jobs ?? please help me about this and if u have any suggestion how can i save some taxes please let me know about it too ...i am working as full time employee in a meat company and doing a part time job on weekend ..
thanks

the amount of tax that is taken off varies with the tax bracket you are in (this can vary pay cheque to pay cheque)