How do Elves meditate?

Elves don't need to sleep. Instead, they meditate deeply, remaining semiconscious, for 4 hours a day. (The Common word for such meditation is "trance.") While meditating, you can dream after a fashion; such dreams are actually mental exercises that have become reflexive through years of practice.

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Also, do elves need 8 hours of sleep?

... a period of extended downtime, at least 8 hours long, during which a character sleeps for at least 6 hours and performs no more than 2 hours of light activity, such as reading, talking, eating, or standing watch. The elf's Trance trait is defined as: Elves don't need to sleep. Consequently, are elves immune to dreams? Elves can sleep and dream just like any human, but almost all surface elves avoid doing so.

Moreover, are half elves immune to charm?

"Elves" are anything with the elf subtype. Half-elves have both the human and elven subtypes, so therefore they are immune to anything that elves are immune to. What spells dont work on fey? Spells/Class Features that fey are immune/can't be targeted Animate Dead. Calm Emotions. Ceremony. Charm Person. Crown of Madness. Dominate Person. Finger of Death* (immune to rise as a zombie only) Gaze of Two Minds (Warlock)

Keeping this in consideration, are elves fey?

Though they are humanoids, all elves are descended from fey creatures, as suggested by their Fey Ancestry trait. In addition, as you quoted, the eladrin are closer to their fey ancestors than most, as they are native to the Feywild itself (rather than the Prime Material Plane).