The adjective "global" and the adverb "globally" are synonyms of worldwide and mean of or relating to or involving the entire world in the general sense or as the planet Earth. In the common parlance, it also is used as a synonym of generic, general or covering all aspects of the real or an abstract world of interest.
From the geo-political perspective, it is frequently consdered synonym of international/internationally but this usage is not recorded in dictionaries and is usually considered incorrect.
Nonetheless, "global" has passed into common usage, especially in the media, academia, and the business world, and among left-wing supporters of a "one world" concept. Many use this term in situations where "international" would clearly be the more appropriate term, as there are few things that are truly global (even the much-touted "global economy" for example does not include Antarctica, North Korea, etc.). Nevertheless, just as its synonym "worldwide", "global" is often appropriate when one wants to emphasise that something affects the entire world even if not all nations or all parts of the earth are directly included. For example, Antarctica and North Korea and even isolated jungle tribes are very strongly affected by the global economy even if they do not actively participate in global trade.
The usage of "global" is correct when referring to things which do involve the Planet Earth as one single unit, for example: global maps, global weather patterns, global satellite photos.
Global can also mean total or universal, as in the phrase "global skepticism", which in philosophy means that the skeptic is skeptical about literally anything and everything, including their own existence, their own thoughts and experiences, and even the existence of an objective reality (universe), i.e. of anything whatsoever. Other, non-philosophical useages have probably extended from this.