I have my CDL, and in a previous career I used to drive trucks. Driving a manual in a semi truck is sort of like driving any other manual vehicle, except, you only clutch to get into gear and clutch to get out of gear. When you drive a truck, you float gears, meaning no clutching in and out like on a normal passenger vehicle/light truck. You change gears when you let off the fuel pedal and let the transmissions sync and mesh the gears itself. As far as the gears, it is known as HI/LO splitting. For instance, there are still 6 gates (sometimes I call it an L shifter 7 on very rare transmissions), but you have a switch that you flick up and down for your HI/LO splits depending on your load. If unloaded, you pretty much stay in HI and depending on the gearing and HP, you can skip shift quite a bit. 13 speed vs 18 speed ain't much different, you just have more HI/LO options for heavy loads or more HI/LO reverse options. Depends on the vocational purpose of the truck.
One can float gears on a passenger vehicle doing the same method, but it is ill advised. Not good for the synchros and the gear meshing cuts really isn't designed to be float shifted. However, there was one time I had to float shift a passenger vehicle and that was went the slave cylinder decided to spring a leak. Was a challenge, and a lot of gear grinding, but I made it.
A good truck driver can float gears so smooth that it doesn't sound like a slap shot from a hockey stick going on inside the transmission. Less of that will only make the transmission last a lot longer. Same with lugging, that is both hard on the engine and transmission and wastes fuel.
Now a days, a lot of these new trucks have semi-automated or fully-automated (automatic) transmissions. They work like the conventional manual transmission, but just use a solenoid to make the gear changes. Automatic neutral and stuff like that. Still totally different than passenger cars.