I have used an accountant to run my payroll last yr. I dont want to use one this yr. I am a single member LLC?

I want to earn Socialy security credits, Hence want to run a payroll anually. I pay estimated tax. Can I run my own annual payroll? I want to run it manually. No s/w please. If I know the Medicare, SS, FUTA tax percentage guidelines, Can I do it myself? pls explain with an example. ume my gross salary is $4000. Can you break it down and let me know my net Income. Thanks in advance