So I have read some stuff about how to do this, including using a carpenter square which I have, but I am not sure how to go about doing it. I have some pieced blocks and some that are appliqued and I intentionally did the appliques bigger than needed - so how do I square it up and have the applique be centered? I don't know if I am making sense - I am very new to quilting and am not sure on a lot but you all are so very helpful. Thanks in advance.

If you have a square ruler the size you want the block to be, it's easiest. The rulers have the center marked, so you put the center on the center of your applique, line up the diagonals and cut around the ruler.

using a larger ruler you line up the 45 degree line from one corner to the other. then trim the side and top and turn your block, line up again and trim the other edges to size.
http://www.quiltuniversity.com/squaring_up.htm
http://www.youcanmakethis.com/blog/5...right-way.html

Square up rulers are an awesome investment. I have a 6 1/2" and a 12 1/2". You would center the applique in which ever size portion of the ruler you are using, cut around two sides and then move the ruler, center and cut the last two sides.

I have a larger squaring ruler which I use most of the time. Like everyone already stated, squaring is not as easy as lining up one side and whacking off what hangs over.

In the beginning, I marked my size on the ruler with small pieces of painter's tape so I would not line up the wrong measuring line.

A lot depends on the block. If there are any points that need to match up with something else, you want to make sure to line up 1/4" away from the points and square to those. The trick is doing this along all 4 sides.

Don't worry - it all comes easier with practice and the carpenter's saying "measure twice - cut once" applies here too.

For pieced blocks, it isn't always possible to trim for evenness. In that case you can "block" the block with starch. Blocking can stretch a too-small block and can also shrink a too-large block. Sharon Schamber has some good Youtube videos that show how to do both.

I have several different sizes of quilting squares to use in squaring up but sometimes they can get quite expensive. On one of the threads someone said that they have theirs cut from plexiglass at Menards and or Lowes. They don't have markings on them but they're a lot cheaper. A 16 1/2" square quilting ruler can run about $35. You can always make the smaller blocks bigger by adding a narrow border. It can make the blocks stand out--like framing a picture--and can really add interest to your quilts. Experiment and find what suits you best.

You mention a carpenter's square. Is this the tool you intend to use to square your blocks?

You have gotten several good answers, there's not much I can add to it.Getting your blocks square is so important to a successful quilt. I hope after watching the videos, all your questions are answered. If not, you know where we are.
Welcome to the wonderful world of quilting and this board.

Ditter

It is worth every penny to buy the square rulers to square up your blocks. The diagnonal line is the key to a perfectly squared block. But as others have cautioned,Don't press your block out of square to begin with, or you will have a mess of your design.