The requirement for paying tax varies from country to country. I can see from your profile that you are in South Africa. Even though HubPages is a US based website, it is the South African authorities who would determine your tax liabilities.
I’m in the UK and here there is a requirement to notify the tax authorities of self-employment status within 3 months of starting. Then at tax year end, I have to submit a return of my earnings for that year. If it is below a certain figure then no tax is due.
If you are concerned about your tax status, why not phone your local tax office’s helpline? Mine have always been very helpful and I expect yours would be too.