As Express Entry draws/invitation rounds occur, the highest ranked candidates who meet the cut-off score (determined each draw) are issued an Invitation to Apply (ITA) which allows them to submit a complete application for permanent residence.

Being accepted into the Express Entry pool does not guarantee that you will be invited to apply. Only the highest ranked candidates when a draw occurs are invited to apply for Canadian permanent residence.
You will learn more about what you can do to increase your CRS score and maximize your chances of being invited to apply in module 6 (How to increase your CRS score).
Gaining more work experience or improving your language test scores can have a tremendous impact on your CRS score.
If you are invited to apply, you will receive a message in your account telling you:
After receiving the ITA, you will have 60 days to submit an application for permanent residence.
You will have to prove that the information submitted in your application (by uploading additional supporting documents) accurately reflects the information that you provided in your Express Entry profile.
The final stages of the Express Entry process can essentially be broken down as follows:

Receiving an ITA does not automatically mean that you have been accepted as a Canadian permanent resident. The ITA simply allows you to submit an application for permanent residence. Once an application has been submitted, it undergoes a review process before a final determination is made.
Now that we have had a chance to learn about the Express Entry pool, the CRS, and the ITA, let’s discuss what documents you will need to prepare for this process.