How to create Knowledge Base articles in the Service Hub using best practice.
Knowledge Base is a repository for all of your commonly asked questions and articles which may be of interest to customers on an ongoing basis. You can direct people to different articles inside your Knowledge Base from your website, Service Hub, Facebook Messenger and any channel you may use to communicate with your customers.
To access and manage your Knowledge Base, go to the Service tab in Hubspot and find the Knowledge Base under the Service drop-down menu (see image below). This link will take you to the Knowledge Base Insights tab where you will see a dashboard view with some useful statistics on your Knowledge Base articles.
To add a new article follow the steps below:
In your Knowledge Base, click the Create Article button (in the top right corner of your screen)
On the following screen (under the Write tab), fill in the missing Title, Subtitle and Answer. These refer to the topic you want to cover or a frequent customer question you want to answer.
Make sure to write in plain language and follow the suggested format of HubSpot so that your article is user-orientated. 
Click the Settings tab to set the article URL and select the appropriate Category the article will sit under.
Categories are a really important element in helping customers to find solutions quickly and efficiently. We suggest reviewing your categories on a regular basis and ensure that they align with the way your customers are interacting with the Knowledge Base.
Select the Preview button (top right corner of the screen, under the Publish button) to see what your article will look like once finalised. Do not publish your article until you are happy with the way it looks and the settings are complete and finalised.
Further Resources
HubSpot: Creating Knowledge Base Articles
HubSpot: Migrating an existing Knowledge Base