Using this example:
Cell A1 contains Name and Street Address. Cell A2 contains City,
State and Zip. You want the contents of cell A2 appended to the
contents of cell A1.

Highlight cells A1, A2 and holding the mouse button down, extend that
highlighting over several cells to the right enough. You do this to
accomodate enough room for the appended text to fit on the screen.
Don't worry - it will all go into cell A1 - you just need to create a
highlighted area for the text to fit into. (You could also do the
same by simply making column A extra wide temporarily to fit all the
text in and then returning it to its original widith afterwards, but
that's not really necessary.)

Using the example above, I highlighted cells A1 through J2. I could
have gone to M2 or S2 - makes no difference - you just want to
highlight over a bunch of cells over to the right.

Now, do EditFillJustify, and assuming you've highlighted enough
space, all your text will be now appear in cell A1.

The more lines you need to append, the more highlighting over and down
you'll need to do. If it doesn't all append the way you want, it
means you didn't have a sufficient number of cells hightlighted to
accomodate the text. Experimentation is the key.