How can I invoke a recording inside of another recording?

I’m new to rpa express, so this question may sound dumb to some, but so far I have created a few recording, now I want to create a Main recording that invokes the other lower lever recording as is needed. How can i do that?

There is no option to invoke recordings inside another recording.
You can publish all your recordings to Control Tower and create a business process out of them.

You can find a guide on how to do it in the Knowledge Base
https://kb.workfusion.com/display/RPAe/How+to+Create+Business+Process