Not sure which transistor tutorial you read (a link would be helpful so that I can read the exact same one).
If this is on Bi-polar transistor, NPN & PNP types, then these are turned on with current flow through the base and emitter. The voltage required is about 0.6V due to the emitter diode but it is the current that turns on a bi-polar transistor.
If the tutorial is on MOSFET transistor then a voltage applied to the gate turns on the MOSFET. For an N-channel the transistor turns on when the gate voltage is higher than the source. The threshold voltage is different on different MOSFETs therefore one needs to refer to the data sheet for the MOSFET being used. Many will turn on with the gate 5 Volts greater than the source but other may need as much as 10 Volts.
Either a Bi-polar or MOSFET transistor can be used to invert the LED drive. Which type did you read about?