When people say trading what are they referring to? Are they talking about trading physical idem's for bitcoins or are they talking about going to something like Yobit and trading alt-coins to get bitcoins . Please explain what everyone is taking about in more details please.
Most likely, people mean trading bitcoins for fiat. On European exchanges people trade bitcoins for dollars and euro, such as BitStamp and BTC-e. On Chinese exchanges it is dollars, for example, at Bitfinex, and yuan on the majority of other exchanges located in China. Minor local exchanges may be trading their local currencies, obviously.
There are also a few altcoin exchanges such as Bittrex and Poloniex