If you are using an alpha or a kit where the embellishment pieces are all on one page, Here are some simple steps for using these alphas on your layout:
Open the png Alpha file.
Select your Marquee OR Lasso tool (whichever you prefer).
Click & drag your marquee (or draw your lasso) around the letter you wish to use. It should now be an active selection (marching ants around it.) Get the Move Tool and drag the letter onto your layout. It will be added on its own layer.
Repeat the steps for additional letters.
If you accidentally select part of a neighboring letter on the page, simply hold down the Alt (PC) or Option (Mac) key and draw a new marquee/lasso around the part you want to subtract it from the selection.
If you need to add more to your selection, hold down the Shift key and marquee/lasso the additional part of the image to add it to your existing selection.
If you want your letters to be centered on your layout, hold down the Shift key as you drag it from the png file to your layout.