Well, basically, traditionally, plane wings were horizontal. Then, manufacturers realised that you improve aerodynamics (and thus also range and fuel efficiency) as well as stability I believe if the tip of the wing "goes up". You have different types of designs:

- winglets are typically fixtures with an upwards angle that were I believe first popularised on large passenger aircrafts with Airbus A310s in the 1980s, and that you still find (for example) on 747-400s since the mid-1980s, and also on A330s and A340s.

- wingtip fences are also fixed to the end of the wing at an angle but they really have a delta type shape (a bit like an arrow head) which goes partly above and partly below the wing. They are used on many airbus families such as the classic A318/19/20/21s and A380s.

- blended winglets face upwards (like regular winglets) but they are curved rather than straight angled. New generation B737 (which first introduced them), B757, and B767s all feature blended winglets as do Embraers E70s and E90s. In 2012, Airbus invented "sharklets" which are a particularly efficient form of blended winglets (saving about 4% fuel) and which equips their A320 NEO range.

You have other options too. 787s use "raked wingtips" which basically play around the shape of the whole wing instead of its extremity and A350s will use "non planar wingtips" which effectively work as a series of upwards angles in the wing. Neither 787s nor A350s need winglet as a result. I am sure there are plenty of new systems being researched or implemented too and that some people with greater technical ability than me will correct my rather pedestrian description of the above different systems.