The actions menu contains all of the functions that allow you to add or create new items. Basically you can think of this menu like this: it contains anything that you want to do that is a "Verb", excluding the items that are on the Modules Menu such as Create Purchase Orders. The actions menu is on every top level record type and some of the menu items are in common with all top level record types such as add a note, add a follow-up, attach a document, and add a phone message.
This should be the first place you look when you want to perform an action on a company.
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