P1 and P3 are special function registers that are treated as variables.
Px = var
var = Px
The number of the port. (1 or 3). P3.6 can't be used with an AT89C2051!
The variable to retrieve or to set.
Note that other processors can have more ports such as P0, P2, P4 etc.
When you select the proper .DAT file you can also use these ports as variables.
In fact you can use any SFR as a byte variable in BASCOM.
ACC = 0 'will reset the accumulator for example
See hardware for a more detailed description of the ports.
Dim A As Byte , B1 As Bit
A = P1 'get value from port 1
A = A Or 2 'manipulate it
P1 = A 'set port 1 with new value
P1 = &B10010101 'use binary notation
P1 = &HAF 'use hex notation
B1 = P1.1 'read pin 1.1
P1.1 = 0 'set it to 0