Both are attempting to get information on the history of events.
The primary difference is that absolute dating assigns an actual time or age to an event or object.
Though relative dating can only determine the sequential order in which a series of events occurred, not when they occur, it remains a useful technique especially in materials lacking radioactive isotopes.
Relative dating by biostratigraphy is the preferred method in paleontology, and is in some respects more accurate (Stanley, 167–69).
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.
By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.
The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah is a great example of Original Horizontality and the Law of Superposition, two important ideas used in relative dating.
Picture from Glen Canyon National Recreation Area, Utah.
Relative dating is the science determining the relative order of past events, without necessarily determining their absolute age.
The Law of Superposition was the summary outcome of 'relative dating' as observed in geology from the 17th century to the early 20th century.
Short Answer: Both relative dating and absolute dating are tools used to give temporal characteristics to a sequence of events.