Migrating your site from a non-WordPress portal to WordPress could be challenging. It is not always easy to bring all the articles and users from your old site to your new site. But there are tools you can use to make the process easier. Import Users from CSV is a cool plugin that lets you add usernames to your WordPress database by importing them from a CSV file.
This plugin imports all user fields and meta data. It also lets you set roles for each user. You can send notifications to new users if you wish. You can also use a CSV file to update your existing users (just to update certain fields). Pretty nice plugin to use to save yourself time importing usernames to your database.