Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal of the source. This was the convention chosen during the discovery of electricity. They were wrong!
Electron Flow is what actually happens and electrons flow out of the negative terminal, through the circuit and into the positive terminal of the source.
Both Conventional Current and Electron Flow are used by industry. Many textbooks are available in both Electron Flow and Conventional Current formats.
In fact, it makes no difference which way current is flowing as long as it is used consistently. The direction of current flow does not affect what the current does.
In general, two year technical programs and highschool Physics use Electron Flow.
But three year technician and university engineering programs still use Conventional Current. Certain symbols (ex. diodes and transistors) and rules (ex. Right hand rules for electromagnets) were created using Conventional Current. Changing from Conventional Current to Electron Flow would cause a degree of confusion for old and new students and errors would occur, so Conventional Current was kept to ensure there was no confusion.
Throughout this course, Conventional Current is used. Therefore always assume current flows out of the positive terminal of the source.