The plain explaination is 这是什么. But in Northern China, people always use 啥 or 嘛 to replace 什么. If you say 这是啥 or 这是嘛, Chinese people will find it funny but amazing because it's a very colloquial and native speaking way.

You can say "我支起了帐篷" or “我把帐篷支起来了”. In Chinese, we always use a "了" to describe an action which is short and done.

喆有很好的寓意，但不是一个常用字，很多人会误读为“吉”，更让我觉得恐怖的是我的iphone居然打不出“喆”字...

之 is a very old word in Chinese. There are some terms used today like 之前, 之后, 之所以, and some idioms like 求之不得, 意料之中. Except those, we seldom use 之 in informal conversation, because an alternative can always be found to replace 之。 What Luna wrote is specific, but I'd like to give you some explanation of 之 in this phrases. 由京之沪：here 之 is a verb, means 去 到. We can also say 从北京去上海 or 从北京到上海. 求之不得：here 之 is a pronoun, means sth, which is a normal way to say "it". 意料之中：here 之 的doesn't have a exact meaning. 那是意料之中的事=那是意料中的事. Here 之 is like 的（of）. 之 is also a normal way to say 的. XX之座驾 means someone‘s horse or car, which is equal to "某某的座驾".

I'm not sure about the differences between 'nerd', 'dork', and 'geek‘, but I think 书呆子 and 宅男 are different in Chinese. 书呆子 is an old saying and often used to describe someone who is smart (but not extremely smart) but too addict to reading books and believing what he reads. Mostly, when we call someone 书呆子, we don't mean to critisize or judge him. It's just an figurative or ironic way to show opinions and care. 宅男, which is what "geek" means, is a new word in Chinese and originates from Japanese. You know 宅 means HOUSE, so 宅男 means guys who spend most of their time at home instead of going outside for exersices, meals or tours. However, now 宅男 is more like a cultural sign and stands for a certain group of people who shares the same interests in cartoon, entertainment stars and so on. You don't have to actually stay at home all the days to be a 宅男, but being a 宅男 requires some certain characters.