[1] Transitions provide greater cohesion by making it more explicit or signaling how ideas relate to one another.
While they are used primarily for rhetoric, they are also used in a strictly grammatical sense for structural composition, reasoning, and comprehension.
In simple terms, a transition word demonstrates the relationship between two portions of a text or spoken language.
[3] Transition words and phrases categories include: Conclusion, Continuation, Contrast, Emphasis, Evidence, Illustration and Sequence.
[7] The transition words, such as also, in addition, and likewise, add information, reinforce ideas, and express agreement with preceding material.