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Also, why do the tips of airplane wings turned up?

Called winglets, the curled tips shrink the vortices at the end of the wing, which in turn improves its fuel efficiency. What's cool is that this wingtip design is stolen from nature: birds curl their wings when they fly.

Subsequently, question is, why do 777 not have winglets? B777 was designed when the advantages of the wingtips were well known, yet they decided to go without one anyway. Because winglets are a tradeoff: In the highly visible case of the 777, an airplane with exceptionally long range, the wings grew so long that folding wingtips were offered to get into tight airport gates.

Subsequently, question is, how do winglets reduce drag?

Designed as small airfoils, winglets reduce the aerodynamic drag associated with vortices that develop at the wingtips as the airplane moves through the air. By reducing wingtip drag, fuel consumption goes down and range is extended.

Why does 777x have folding wing tips?

Boeing's new 777X extends its folding wingtips to complete first flight. The aircraft's design is intriguing: Folding wingtips will let the 777X fit at existing airport gates while still giving the wings the lift they need.