An introduction to an essay usually has three primary purposes:
To set the scene
To tell readers what is important, and why
To tell the reader what the essay is going to do (signposting)
A standard introduction includes the following five elements:
A statement that sets out the topic and engages the reader.
The background and context of the topic.
Any important definitions, integrated into your text as appropriate.
An outline of the key points, topic, issues, evidence, ideas, arguments, models, theories, or other information, as appropriate. This may include distinctions or contrasts between different ideas or evidence.
A final sentence or two which tells the reader your focal points and aims.
Leave your questions regarding writing introductions in your comments below.