The following information is based on OS X 10.10 Yosemite. If you are running an earlier version of OS the information might still useful but you may have to look in different settings.
OS X has three account types – Administrator, Standard, and Managed (with Parental Controls). The Administrator account is the most important.
Standard: Standard account users cannot administer other accounts, but can install software for their own use and change settings related to their accounts.
By default the OS X Setup Assistant configures the first account on the Mac as an administrator account. This account can do anything to the Mac including installing software and changing system settings and other accounts. It’s a bad idea to use this regularly for day-to-day tasks and Apple recommends that users should use standard user accounts for day-to-day computer use and create an Administrator account strictly for system administration tasks.
The important distinction between a Standard and Administrator account is that the Standard account cannot make system wide changes or install software for use by other users on the Mac.
Create a new Standard account
The first step is to create a new Standard account. You can do this by launching the System Preferences application and then clicking Users & Groups. You will be taken to a preferences pane that looks something like this.
You may have to click the lock icon in the lower left of the screen to make changes.
Click the + button in the lower left corner to bring up the new account dialog. Choose Standard from the drop down and enter a name for the account. Enter a strong password and make sure to write it down and store it somewhere safe.
Local OS X Yosemite accounts can use local passwords for authentication or can be linked to an iCloud account. Once linked, the user can login to the Mac using the same password they user for their iCloud account.
User names like “Khürt Williams” or “Khürt” are helpful but feel free to be creative. If you are a fan of the Lord of the Rings Trilogy, perhaps "Frodo Baggins" is a good choice for you.
Click Create User and voilà, you have a new Standard account. To customize the account, clock the image icon and choose and image from the defaults or drag one from your hard drive on to the icon to change it.
Once the new Standard account has been created, please logout and log back into the new account to test that the password works.
I know that using an account with Administrator privileges makes it easier when installing software or making system changes. However, these are activities that the average users has to rarely complete. Performing your day-to-day work using a Standard account reduces the likelihood that you accidentally install a Trojan horse or some other malicious software.