[SOLVED] How does the glue tool work?

I’m attempting to glue midi clips together, but no matter what I’ve tried, the icon for the glue tool is always grayed out.
I’ve googled it, but nowhere can I find an explanation of how the tool is supposed to work.
Could some kind soul please explain how the tool is designed to work? I’m not a new computer user, but this issue has baffled me.

thanks for any info

You have selected all of the parts you are trying to glue?

…plus you need to close the key editor first,
then “select” at least 2 regions on the same track…

Thank you both for taking the time to reply. The piece of information I was missing: close the key editor! Then multi-select works (after touching the select icon first)