At first install the extension from chrome webstore

After installing the extension, pin the extension from top-right buttons in chrome then you will see the Pockets icon of your Chrome browser. Click on the icon to open the extension popup.

A setup required screen will appear. Go to the settings page by clicking on the settings button.

You can create a project in two ways:

From the extension: Enter your email and a project slug in the registration form, then click "Create Project". Your API key and project ID will be saved automatically.

From Pockets API: Visit Pockets API and register with your email and project slug. Copy the API key (shown only once) and paste it into the extension settings along with your project slug in the Project ID field.

After filling the fields, test the connection if you want, then click on the save button. Now you are ready to use the extension.
Go back to the popup and start saving links by clicking on the save button.