In short:
/e/ is basically LineageOS tweaked for more privacy and with a selection of pre-installed Apps which should make it seamlessly usable by about anybody.
Lets boldly and simply say you could give a phone running /e/ to your parents or grandparents with much less hassle afterwards than you would have if you gave them one with LineageOS.
In halfway short:
/e/ take LineageOS as a base, throw out as much Google stuff as they can still find to improve privacy (which is not the top priority of LineageOS), and then add
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Bliss, an iOS-like launcher (of course you can install a different one if you don’t like it)
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microG, which uses Open Source software to mimic many Google services and components, so many (but by far not all) Google-dependent Apps can happily work without Google
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Apps which are intended to make the system appealing to and seamlessly usable by the average smartphone user (prime examples: Magic Earth as a reasonably straightforward and usable Google Maps replacement, and an easy-to-use App installer which has many cost-free and wide-spread Google Play Store Apps to avoid death by “App gap”, along with F-Droid’s Open Source App collection for the users who like these better).
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an Open Source based syncing service resembling the Google cloud, with the possibility for you to self-host it.