This article shows the steps to add the Content Editor web part to SharePoint online site.
Content editor web part is used to display your rich content and custom functionality.
Prerequisites create a trail Office 365 E3 license account.
Just follow the below steps,
Step 1
Go to the SharePoint admin center --> Active Sites, click create,
Step 2
Select "Other Options"
Step 3
Choose More Template from the dropdown
Step 4
Fill in the Title, web site address and add your admin name if your the admin add your name
Step 5
Now go to site contents --> Site Pages --> New --> Web part page
Step 6
Give your page a name, select the layout and destination as site pages
Step 7
Add Content Editor Web part
Step 8
Add your HTML file from Site Assets to the web part
Once added click "Stop Editing", your page is ready!!!