LATB is a register within the PIC, not a PBP command. Exactly the same as TRISA, CMCON, WPUA, ANSELA, ADCON and a few hundred more that you will not find in the PBP manual but rather in the datasheet for the specific PIC you're using - again because they are not PBP commands but registers in the PIC that you can read/write.

LATB.0 = 1 is the syntax used to set bit 0 of the LATB register to '1'.

Not all PICs have a LAT registers. On those who don't you need use the PORT register instead.

NOP is the assembly instruction "No Operation" which "wastes" one instruction cycle. @ is the inline assembly directive used to tell PBP that the rest of the line is in fact assembly and not PBP commands.