Neither the conclusion, nor the introduction, should totally summarise your whole argument: if you try this, you are in danger of writing another assignment that simply repeats the whole case over again.
You must include a reference list or bibliography at the end of your work.
How much evidence you use depends on the type of essay you are writing.
If you want a weight of evidence on some factual point, bring in two or three examples but no more.
If you have read other documents in order to contrast your argument then these should also be referenced.
When writing an essay it is good practice to consider your reader.
Essays are generally a blend of researched evidence (e.g. Some students' essays amount to catalogues of factual material or summaries of other people's thoughts, attitudes, philosophies or viewpoints.
At the opposite extreme, other students express only personal opinions with little or no researched evidence or examples taken from other writers to support their views. The balance between other researchers’ and writers’ analysis of the subject and your own comment will vary with the subject and the nature of the question.
To guide the reader through your work you will need to inform them where you are starting from (in the introduction), where you are going (as the essay progresses), and where you have been (in the conclusion).
It is helpful to keep the reader informed as to the development of the argument.