How To use ANDWF in Microchip PIC18fxxxx Assembly Language
The IF, AND, THEN and END IF in your code are all statements affecting program flow, not mathematical operators. 

The PIC18F2550 has an instruction CPFSEQ (compare w to f, skip next instruction if equal) which can be used to implement the AND function in your example, like this:-

_if:
  MOVLW  0
  CPFSEQ Variable_1  ; IF Variable_1 = 0  
  GOTO   _endif      
  MOVLW  1
  CPFSEQ Variable_2  ; AND variable_2 = 1 
  GOTO   _endif      
  .
  .                  ; THEN do what is needed       
  .
_endif:


Note: this code just shows the principle, and may not be the most efficient (eg. using TSTFSZ Variable_1 and BRA _endif would be faster and more compact).