[Imp]

Yes you must be

The load all button will attempt to load everything it can during the deployment phase.

When using the L button to load a unit you
1) select a unit (the one you want to load is best
2) Press the L button
3) Now select the unit you want it to load onto

As said both units should be in the same hex.
It doesn't mater which company or platoon either unit is in, it will load the unit if it fits.

To unload just press the L key on a unit with passengers