The Webster dictionary defines the noun, “textual criticism” as, "the study of a literary work that aims to establish the original text.”  This works as a starting definition, but may oversimplify the discipline if we were to stop there. NT Textual Historians Bart Ehrman and Michael Holmes describe textual criticism(also called lower criticism), for the New Testament, involves “…a complicated set of disciplines, many of them in rapid transition.” They go on to lay out that many sub areas of NT textual criticism involves:
…Greek manuscripts (…papyri, the majuscules, the minuscules, and the lectionaries), the early versions (Diatessaron, Syriac, Latin, Coptic, Ethiopic, Armenian, and Georgian), patristic citations (Greek, Latin, and Syriac), studies of scribal habits, approaches to manuscript classification, the use of computers for textual criticism, recent apparatuses and critical editions, methods for evaluating variant readings (the Majority text theory, thoroughgoing eclecticism, and reasoned eclecticism), and the use of textual data for early Christian social history…
A Greek Papyrus
1000 Bible Images. Stuttgart, Germany: German Bible Society, 2009.
With all these sub areas and more that are considered to try get to what the autographs (the Greek is αὐτόγραφος, which means “written in one’s own hand”) actually said is a complicated manner.
However, textual criticism has been going on possibly since the time of Origen (about 250 A.D.) so there has been time to develop mostly coherent methods to navigate through the complexity outlined above.
Textual criticism has great value for this is the science to getting to as close as we can get to the revealed word of God (2 Tim 3:16, 2 Peter 1:21, Matthew 4:4) for us, with the guidance of the Holy Spirit, to translate, exegete, interpret, and apply to our lives as best as we can. Without textual criticism, we have gibberish.