Transitions are words or phrases that carry the reader from one idea to the next. They help a reader see the connection or relationship between ideas and, just as important, transitions also prevent sudden, jarring mental leaps between sentences and paragraphs.
You should use transition words to transition your ideas.
For example, if you are talking about why people should eat apples, you could say that, Apples prevent the risk of getting heart disease, and then you explain that. Now you want to talk about how apples prevent the risk of diabetes, to do this you need a transition word, like also.
Apples prevent the risk of getting heart diseaseapples prevent the risk of diabetes.
Apples prevent the risk of getting heart diseaseAlso, apples prevent the risk of diabetes.
Hope this helps!