If the text is in columns A & B and column C is empty
in Cell C1 Create the formula =A1&"."&B1
Substitute the actual row you are on, in the formula
Copy the formula down as many rows as necessary
Highlight all the formulas Select copy then Paste special choose values
This will convert the formula's You can even paste them over column A if you want
To add text to a column you can still use the above method.
Place an & in front of the text and enclose it in " " marks.
example in column C =A1&" This text will be appended"
If you want to use Jeni's method I would insert a column between the two you want to merge and fill it with a dot in each row. That would save editing each row after the merge.
Jeni's method has the advantage of not needing extra columns, but the disadvantage of only working with one row at a time.