Yes, to what Carol said. More simply said, it's a fabric glue that looks like a thin web that you iron onto your fabrics. Ironing instructions come with most of the fusibles you can buy and there are different instructions for different types of fusibles.
Some fusibles are designed for "no sew" projects and believe me, they mean "no sew"...to sew thru these you tend to break needles, or gum up your needle so bad you can't sew with it. Others are designed for sewing projects and even they come in different weights...the heavier ones make your project very stiff, and lighter ones are almost non-existent once your project is done.
For your project you definitely want a sewable fusible...and the bolts should clearly say which is which. You can purchase them at any store that sells fabrics.