It is the procedure through which a person registers as a self-employed person in Social Security, thus beginning their economic activity on their own account.
This involves a monthly payment of the self-employed fee, which varies depending on your income.
Here you have the section system.If the first time you register as a self-employed person you have a reduced fee of €87/m. Depending on your Autonomous Community, it could be reduced to €0 if you meet the requirements of the zero fee.