The introduction to an IELTS writing task 1 essay should explain what the chart/graph shows. To do this, just paraphrase the question (rewrite it in your own words).
Here is an example description from an IELTS Task 1 question:
The graph below shows the proportion of the population aged 65 and over between 1940 and 2040 in three different countries.
By rewriting this description with a few changes, I can quickly create a good introduction:
The line graph compares the percentage of people aged 65 or more in three countries over a period of 100 years.
If you practise this technique, you will be able to write task 1 introductions very quickly. You will be able to start the writing test quickly and confidently.