Magento Connect (Magento Marketplace) is a marketplace that allows Magento community members and partners to share their open source or commercial contributions for Magento with the community. Typical contributions include:
Magento Connect allows you to connect to the wealth of Magento extensions available, some of which are free, and some you have to pay for.
Community Extensions: Open source extensions created by Magento Community members or partners that are released under an open source license.
Commercial Extensions: Contributions available for purchase by Magento community members or partners. Commercial extensions may be sold, distributed, and licensed directly through the seller.
First you need to log into the Magento administrator area, and then go to
System > Magento Connect > Magento Connect Manager . This screen will appear:
Try to login with admin account and you can see
Now to go Magento Connect to get an extension key. In this post, I take an example: Better Blog extension by Mageplaza
Here are key
Then paste the key to install and click
Install button, then click
Process to download and install the Better Blog extension on your Magento store.
Ref: Magento 2 User Guide
It comes to the end of tutorial: How to install Magento Extension from Magento Connect Marketplace.