Help!! This is the first time I have chosen backing fabric with a pattern... and I have to make a seam to get the backing large enough. I have looked at some tutorials.. and I am CONFUSED. Anyone have a simple hint? Or point me to a more simple tutorial that I may have missed while searching? Thank you in advance...

The lady who does my backings and quilting just cuts it into legnths adding the extra inches i believe it will depend on the size of quilt and fabric you bought. if you cut the fabric legnthwise or accross and sewing it together.
depending on how its quilted some of the seam can be blended in. when your gazing at the quilting you might even miss the seam. hope this helps
good luck Sandra

It has a specific plaid pattern... :-/ I think I have to match it exact (or close too). I folded one side and pinned it to the other side... but how do I sew it?

Cut the pieces to the approximate size - I think you already have. Put right sides together with a strong line of one side close to the same line on the other. Put a pin through the top stripe and then through the same stripe in the bottom layer. Do this every few inches and then sew it. Be sure to check several places. If it is not a balanced plaid, a line can match, but the plaid doesn't match.

This might also be a good time to use the glue basting method. I've never used it to match patterns but I know that it works wonders on matching seams. I use a washable fabric glue then set with an iron. It should work well with the plaid.

Ditto! Glue basting and pinning would hold it together while you sew it. This also works great to match prints for borders to give you a seamless look.

I just pin and sew using at least a half inch seam. I don't bother too much about matching the pattern - just try and make sure its all going in the same way if it is a directional print. Always works out fine. I've only used a plaid in a backing once, and even though it didn't quite match up on the seam line, it still looked ok once it was quilted. I doubt if you could get a plaid to match perfectly anyway, because most aren't quite straight on grain, so don't stress!

You might try sewing in into a tube. ( Cut two lengths as required,) place them face to face, matching the plaid on both sides, sew both seams, then cut one side in half. This will give you a finished back without a center back seam. I hope you can understand my explanation.

Or put narrower strips of a coordinating fabric between the plaid panels. This way you wouldn't have to be exact matching the pattern.

All great suggestions ladies! I knew you all would have great techniques. I am off to work, so I will think on it during the day and then tackle it again this evening.