To start analyzing a backlink profile of a site, you need to create a project. Launch SEO SpyGlass and enter a site URL you'd like to monitor. In the same step, you can set the range of results SEO SpyGlass should collect: you can select Domain only, Domain and subdomains, or Exact URL.
Hit Get Backlinks, and the program will take a few moments to gather the backlinks from the selected source(s) and load them to the project, as well as will check the overall domain metrics. Once done, you'll be switched to the Linking Domains section under Baсklink Profile; it will show the list of linking domains found for your site along with basic stats. The Tags column will indicate the source the backlinks have been gathered from.
If some known backlinks haven't been found in chosen sources, or you have just built some fresh links, you can add any URLs to your project manually with the + button in the Backlinks section to start analyzing them right away. You can also remove any backlinks from the project anytime: select the links > right-click to open context menu > choose to Remove backlink(s) from project.
The number of projects you can create and domains you can analyze is not restricted in SEO SpyGlass. Resource-wise, the limitation per one project file is 250K backlinks, but in case many more backlinks are found, you'll see a footnote at the bottom of the workspace stating that there are 'x more backlinks'. You can export the full lists by source (in any paid version) into CSV using the Quick Export button in the Backlinks section.
In the end, you can Save the project, Close it without saving or click New to create another project.