9gag — Go Fun Yourself
9gag is a website on which users can share funny content. It started in 2008. The meaning of the name is uncertain but there are two theories. One is, 9gag is read as "gou gag" in Cantonese (its creators are Hong Kongers), which means "make joke". Other one says that the site had 9 posts on the front page in its early years, that's where 9 comes from, and gag means "joke" in English slang.
Numbers
As of September 16, monthly statistics show 9gag as world's 151st most visited website with 245m visits. Country-wise, it has the highest rank in Germany by #71. Germany also provides the highest number of visits with 7.97%, and is followed by United States (6.33%), France (4.73%), Poland (4.47%), Turkey (4.06%).
Voting and its effects
9gag basically has three categories which are Fresh, Trending, and Hot. Once you upload a content, it goes right into Fresh. Then people can up-vote or down-vote it. If its net number of votes (#up-vote - #down-vote) reach a certain number, it goes up into Trending. Again, if it gets enough number of net votes, it goes into Hot. People can comment on a post, too. However, comments have no effects on the rating of the post. You can up-vote and down-vote comments also, as well as reply to them.
Memes
Majority of the content is memes which are mostly still images. There are literally hundreds of meme types. Some of them are not used as often any more, since new memes emerge in time and become more popular. You might want to take a look at knowyourmeme.com to see what they look like and how to use each.
Thankfully, there is this online meme creator so you don't have to struggle to create one.
Issues that bug me
9gag is a good place to visit if you want to laugh (mostly in the form of NE* though, not LOL**). However, there are basically two issues I am displeased with. One is, people often post non-funny content and they make it into hot. An example is shown in Figure 1. Most of them are not even interesting and makes me question the purpose of the site. The second issue is the same post being posted multiple times (probably by different people and with a time interval between them) and them making into Hot. This would annoy a frequent visitor but occasional visitors wouldn't notice that.

*NE = Nose Exhale
**LOL = Laugh Out Loud