"GND is usually the most- negative point in the circuit. Connect it to -" This can fry things especially if you get involved with analog. Assume GND is your reference point and most voltages plus or minus are referenced to that. Where to you connect the common or ground terminal of your measuring instrument to.
The letter "V" on a circuit stands for the supply voltage. The letters "CC" indicate that the supply voltage is positive or negative and does not indicate any voltage. For most logic items it is 3.5V or 5V but that is not absolute. VCC stands for "voltage at the common collector.
On Qura Naveen Namani, scientific officer at Bhabha Atomic Research Centre (2018-present)
Answered Feb 5, 2018 Basically VDD, VCC, VEE and VSS refer to the supply voltages given to a circuit.
You can identify that VDD and VSS both come in the same circuit, similarly when there is a VCC there can be VEE too.
The difference and the usage came into picture because of the different types of logic families.
For TTL logic gates, we have transistors, and we generally configure them in CE mode. So there is a power supply connected between collector and emitter (generally emitter is grounded or given negative voltage), so came Collector supply voltage (VCC) and emitter supply voltage (VEE).
Similarly for FET based circuits, we have DRAIN terminal, and SOURCE terminal, and in Common Source mode DRAIN is connected to positive supply voltage Voltage Drain Drain (VDD), and source is connected to negative supply voltage (or ground) Voltage Source Supply (VSS).
These voltage levels are absolute in the sense that they are the voltages compared with a common ground, not necessarily all the time VEE and VSS should be zero.
You can find Naveen Namani post at: https://www.quora.com/What-is-a-VDD-in-electronics#
Have Fun Good Luck, Gil