"what's the meaning of a number divide column vertor?"
The mrdivide documentation explains at the top of the page that it will "Solve systems of linear equations xA = B for x". In your example you defined a system of lineaer equations with A = [1;2;3] and B=1, so the output you get is one solution of that system. This is easy to check:
>> A = [1;2;3];
>> B = 1;
>> x = B / A
x =
0.00000 0.00000 0.33333
>> x * A % should be == B
ans = 1
>> 1 ./ A
ans =
1.00000
0.50000
0.33333
To use MATLAB you need to learn the differences between array and matrix operations:
