They have some overlapping meanings.
They can both mean "special":, which means "better or greater than usual". In this case "especial" is not used much.
When different, especial mean "specially", or "made or designed just for a specific person or thing or purpose."
"Especially" means "very much."
So
The book is special because it has color pictures.
The book was made specially for you.
It is an especial book, just for you.
The book was especially long.