While SVGs can be opened, edited, and written in a text editor, there are plenty of applications offering a graphical user interface (GUI) that make authoring complex SVG graphics easier if you come from a graphics editing background. Perhaps the most obvious choice is Adobe's Illustrator (PC/Mac). However, it is expensive for casual users so my own preference is Bohemian Coding's Sketch (Mac only: http://bohemiancoding.com/sketch/). That itself isn't cheap (currently at $99), but it's still the option I would recommend if you use a Mac.

If you use Windows/Linux or are looking for a cheaper option, consider the free and open-source, Inkscape (https://inkscape.org/en/). It's by no means the prettiest tool to work with but it is very capable (if you want any proof, view the Inkscape gallery at https://inkscape.org/en/community/gallery/).

Finally, there are a few online editors. Google has SVG-edit (http://svg-edit.googlecode.com...