SharePoint Designer is an editor used for the management and development of Microsoft SharePoint sites. Office 365 subscribers can download SharePoint designer for free in order to manage their SharePoint online sites. Here we will be discussing how to download and install the software and how to use it to open your SharePoint online sites.
Downloading and installing SharePoint Designer 2013
Log in to your Office 365 account at https://portal.office.com.
Navigate to the portal's home page by clicking on "Office 365" in the top menu bar.
Locate the "Other installs" link that is situated just below the "Install Office 2016" button near the top-right of the page and click it.
On the Office 365 Software page, click on the "Tools & add-ins link in the left navigation bar.
Scroll down to the bottom of the page to find the SharePoint Designer 2013 section and click the "Download and install" link.
This will take you to a Microsoft download page. Click the download button and select the executable that is appropriate for your system architecture.
Install the SharePoint Designer 2013 software on your computer
Opening your SharePoint online sites in SharePoint Designer
In your Office 365 portal, navigate to your SharePoint sites.
Still in the portal, find the site that you want to open in and navigate to it.
Copy the URL from the beginning up to "_layouts/....".
Now open the SharePoint Designer 2013 software that you have just installed on your computer.
Click the "Open Site" link on the Sites page.
In the Open Site window that opens, paste the portion of the site URL that you copied from the Office 365 SharePoint online portal into the "Site Name" text box and click the "Open" button.
After a brief delay while the application connects to the SharePoint Online site, the site should open.