You can find several answers by using Help viewer in your OS X;
some of the items you may find there may reflect to Apple Support.
• OS X: What is "other" space in About This Mac? - Apple Support
• Mac OS X drive content says 'Other'... a duckduckgo search result:
https://duckduckgo.com/?q=Mac+OS+X+drive+content+says+Other&t=ffsb&ia=web
Many of the other items listed in earlier post are copyrighted at the
sites the links go to, so feel free to use them (to see if they help)
from those. You can share them freely to others and disregard the
mention of a previous ASC compiler of them into a single reply.
Since I have all of those bookmarked and clarify each one still works
before I post reference to them; to see if they may be valid, & so on.
{But I would never pledge to shield the content of my posts here from
other helpful direct use by anyone. In other Mac Boards discussions
online over 20 years, my helpful posts (done in an alias name) were
cited in earlier versions of these Apple Discussion by contributors here
but they cited direct links to those original posts in addition copy/paste.
And Kappy was one of the early Mac users I helped on other mac fora.}
The ability to backup a complete computer drive and content is a valuable
feature; you can use Time Machine and OS X Recovery among other helps
to restore the computer (and make bootable full system clones on external
hard disk drives.) One of the sources cited in earlier reply is from here:
• Apple OS X and Time Machine Tips*:
http://www.pondini.org/OSX/Home.html
Since *James Pond was the author to the above content; as his estate has
helped keep it online for other users, the credit goes to him, not Kappy. It
has several layers of content that is helpful to backup and resolve issues.
Though dated, most if not all is still applicable to newer OS X version use.
Other items can be found from detailed online search, or Support articles:
A search engine that does not track you that I find helpful is duckduckgo.
What the "Other" Storage Space is in Mac OS X & How to Clear ... I'm curious
as my iMac has a 1TB internal HD which claims to have 350GB of 'other ...
osxdaily.com/2015/01/15/other-storage-space-mac-o
An externally enclosed drive of 1TB or larger capacity (rotational) would be
slow to read/write; many of them are not fast due to that rotational speed.
If you get one, be sure it is 7200-RPM or faster, and the connection or port
is USB 3.0 or if your MacBook has Thunderbolt port, that is another option
that a modern enclosure can provide; to speed things along between an
external archive and the computer.
See the OWC macsales.com site for examples (you may find similar spec items
locally; but this source has good reputation and reliable helpful staff) even if you
do not buy from them; very Mac-Centric...
• Internal and external storage solutions (hard drive, ssd, flash, etc) for Mac - owc
https://eshop.macsales.com/shop/external-storage
There usually are internal upgrade options, should a user need or want to replace
a smaller capacity storage drive with a larger capacity; some upgrades may require
the help of an authorized trained service tech for best result. An Apple Store may be
a good place to set an appointment with a Genius or a staff Specialist, or consult
an Authorized Apple Service Provider may be able to offer upgrade advice; the
Apple Store may not upgrade hardware on site, but an AASP could.
An external drive with fast data connection should be better especially if you need
to move files in real time to the computer without much lag. Check the specs of
the MacBook you have to see which Thunderbolt port it has; or if USB is 3.0.
Good luck with your situation and bless you...!