merging text fields into 1 field

[Mr DV]

Dear all,

How do I merge text fields of 3 different columns into 1 field?
For example:
A1: 120071
B1: 15
C1: 000
D1: all 3 fields must be pasted to become: 12007115000

What if I would like a dot in between each field? --> 120071.15.000

Thanks!