Transitions in writing is about linking together sentences or paragraphs.
Transition words link sentences together so they flow well and make sense to the reader. Transition words connect ideas and move the concept you are discussion forward, or demonstrate how the points differ.
Just as you transitioned between sentences within the paragraph, you need to transition between paragraphs to ease the flow of your writing and keep your reader interested.
See the Writing Support Center for examples of both types of transitions.