If you are merely needing this for labelling purposes, there are several easy python ways to do it without creating a new field.
If you really need to populate a field with those, make a new text field, then just use the field calculator, select python as parser and make the field = str(field1here) + str(field2here).
Conversely you could make copies of your fields if they are not text type fields, by making two text, new fields and using the field calculator to populate the values in, then create a 3rd new text field and just make it equal to copiedfield1 + copiedfield2