In Windows, if you wanted to type a special character such as the one in the following custom emoticon: =þ, there was the ALT+xxxx format. In the case of þ (the letter thorn in the Icelandic alphabet), the code was 0222. Holding the left ALT Key and typing the numbers in using the 10-keypad was a viable way to do that, but it doesn't work under Ubuntu. What does work however, is Unicode. Unicode is a universal international format that strives to create a standard for writing letters.
In Ubuntu, all you have to do is hold Ctrl+Shift, type U, which will show you an underlined and then you will type the Unicode. For example, to get þ, you would hold Ctrl+Shift, then press U, type 00FE, and press enter.
Now, you're probably telling yourself, "that's great and all, but what if I wanted to put 蠍, the Japanese symbol (kanji) for scorpion, in a text and I don't know the Unicode for it? Well, never fear, the Unicode creators have a handy list of charts in which you can look up special characters and other text obscurities. In there, you would learn that the Unicode for scorpion is actually 880D, or any other character you are interested in. Thinking about creating a new chapter of Tri-Λ? Open the Greek code chart and toss in the code. There are codes for nearly every script in every language, so look for what you need and type to your hearts content!