Do I need MAX232 when using USB-to-Serial cable?
FTDI is the best-known manufacturer for USB-to-UART bridges. "UART" means that the signals are at microcontroller level, i.e. 3.3V or 5V. You can connect such a bridge directly to a microcontroller.

If you want to connect to another computer via a DB9 connector you'll have to add the MAX232, since that connector expects RS232 voltage levels (+12V and -12V).

When we talk about USB-to-RS232 converters, those are USB-to-UART bridges with a MAX232 level converter built-in. They will terminate in a DB9 connector, which is almost always a sign that it uses RS232 levels.