For the rest of your working life, you will receive one of these forms a year from the place you work. In some cases it may be more than one a year depending on if you leave and join another company during the tax year. The tax year runs from March to February of the next year. This form is basically a summary of earnings and deductions you received from the company as well as contributions made in the form of tax, UIF, SDL (on your behalf), medical aid, pension fund etc.
Once a year, during Aug - Sept, you have to submit a tax return to SARS, they already have that info (providing that your company complied and submitted all their returns), but now they have to see what you individually earn and if you have paid your dues (taxes!!!!!).
If this is the first time you are submitting a tax return, it is advisable that you get someone to do it for you, people do it for about R250. If you make mistakes on this return, you may end up having to pay SARS additional tax which is not really due to them.
Familiarise yourself with this process, as I said, it will happen every year, probably for the rest of your life. Don't be intimidated by it, it is just something new and once you're used to it, it will be a breeze!
Good Luck!