Conventional current:
Before 1897, people assumed that the current (electric charge) flows from the positive side of the battery to the negative side of the battery.
Electron current flow:
After 1897, we came to know the actual direction of the current flow.
In reality, the current (electric charge) flows from the negative side of the battery to the positive side of the battery.
To better understand the difference let us draw a simple diagram.
Summary:
Conventional current flow = From positive to negative
Electron current flow = From negative to positive