To check that ASDF is properly loaded, you can run this form:
If it returns a string, that is the version of ASDF that is currently installed. If that version is suitably recent (say, 3.1.2 or later), then you can skip directly to next chapter: See Configuring ASDF.
If it raises an error, then either ASDF is not loaded, or you are using a very old version of ASDF, and need to install ASDF 3.
For more precision in detecting versions old and new, see How do I detect the ASDF version?.
If you are experiencing problems with ASDF, please try upgrading to the latest released version, using the method below, before you contact us and raise an issue.