As the name suggests, anchovy toast is basically anchovies on toast. Commercially-prepared anchovy paste is available, so the recipe can be as simple as spreading the paste on hot buttered toast. More elaborate recipes involve whole canned anchovies, creamed with various ingredients such as onions, garlic, cheese, etc.
Anchovies are small, salt-water fish, from the family Engraulidae. They are gutted, matured in salted brine, and then packed in oil or salt, acquiring a characteristically strong flavour.