1) you do it by following what the processor would do:
addi $t0, $0, 0 # $t0 is now 0
lw $s0, y($t0) # $s0 is now word from memory at address y+$t0 which is 14
lw $t0, v($0) # $t0 is now word from memory at address v+$0 which is y
lw $s0, -4($t0) # $s0 is now word from memory at address $t0-4=y-4=x which is 12
2) y
is a label, it means use y
's address
3) if you only keep v
it should produce a compilation error because y
is undefined (unless your assembler automatically treats undefined symbols as external)