enumerate the key tools of the formalist approach to literature. Do they really enhance our understanding of a literary text

The "formalist" approach to literature really begins with the New Critics. As a group, they were distinctive because rather than simply being academic specialists in theories about literature, many of them were practicing writers, often among the best of their generation. Following in many ways the critical tradition of T.S. Eliot and some of the recommendations of Pound, such author/critics as Allan Tate, Robert Penn Warren, John Crowe Ransom, Yvor Winters, and William Empson believed that rather than looking at authorial intention or historical background, it was important to focus on literary technique such as use of sound devices, meter, figures of speech, allusions, and other literary devices. This is the point of view of working writers concerned with how literary works are actually put together. For some people, especially those who write themselves, this nuts-and-bolts understanding of writing as a craft is very important. For people who are more concerned with literature as a cultural phenomenon, it is less important.
Russian formalism and its structuralist successors were quite different in being an academic movement deriving from the discipline of linguistics. Their search for patterns within works focused on understanding literature as an autonomous rather then referential system. Their work is interesting for the way it can, for example, identify plot arcs independent of content or themes or discover linguistic patterns of different types of narration. This approach is also important due to the way it "defamiliarizes" literature and makes readers think of a story, for example, in terms of what makes it a literary work and its internal dynamics rather than simply reducing literature to social criticism or examples of ideology.