Word won't do flowcharts pre se - you can only have the boxes!
If I make one, I draw a grid using straight lines - then group it so it can be deleted in one go later - then just place the boxes and lines on the grid. If you do the lines first, then the boxes, it's easier to shift the boxes into position (use Ctrl+arrow to get small nudges) and leave the lines behind the boxes. The boxes should, of course, have a white fill for this.
When all is finished, either delete the original grid - or make it white or transparent.
Not the easiest way, but after the first couple of hundred, it gets easier!
Now you watch some rotten so-and-so show an easier way after I've done all the ones that I have!