Linux keyboard shortcuts for text symbols

There are three ways to type text characters, like symbols and special signs, with your keyboard on Linux.

Methods

1. Third and fourth level chooser keys - fastest in use. It's like using the Shift key, which is second level chooser.
2. Compose key sequences - character sequences are very easy to remember, or guess, but the method may be hard to correctly set up, so that they work for all the programs you use. With compose key you can type almost all the useful signs.
3. Unicode hex codes - toughest method. The codes are pretty hard to remember, but you can type any text character available if you know them.

Related

Linux Character mapsType special symbols and text characters with the use of character map for Linux and Unix OS. ❡✽ ➦ ❥ ✪ GNOME's Gucharmap, KDE's KCharSelect Character Selector and Java character map.