You need to have some pattern in mind. You didn't say if the 4" squares are many of the same or all different. But a 4 patch might be an easy pattern to start with. Just sew 2 squares together using a 1/4" seam. Sew another 2 squares together, then sew the sets of two squares together. Start another 4 patch, continue the same way. A common pattern would be one light square, one dark square, then the second row would be one dark, and one light square.
When you have enough 4 patches, sew them together into a long row, the width you want your quilt to be. Keep sewing rows, and then sew the rows together, until you have the length you want.
I you tell us how many 4" squares you have, someone here can help calculate how big a quilt you can make, or how many squares you will need to make the size quilt you want. The squares will finish at 3 1/2", so you can calculate it, too. A baby quilt can be as small as 36 x 45". I like lap quilts to be at least 45 x 60". Then there are bed size quilts.