Letters or other characters saved as vector SVGs can be used for making proper font packages. This is done with some dedicated font editor in which you can import individual vector images and create a WOFF package that can be used by other users in their programs.
Found 2 different conversion types using the same filename extensions.
Conversion svg to woff type 1:
Convert from XML based scalable vector graphics format to Web Open Font Format package file.
On-line services software - convert svg to woff on web
FreeFontConverter is an on-line tool used for free font conversion.
File type (from-> to)
Convert from svg file
XML based scalable vector graphics format
to woff file
Web Open Font Format package file
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned svg to woff. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Online font converter is a web tool that offers conversions of various font formats, including many exotic formats. It should support most of the common formats for Mac and PC.
Conversion svg to woff type 2:
Convert from SVG fonts format to Web Open Font Format package file.
Microsoft Windows software - convert svg to woff on Windows
FontCreator is one of the most popular font editing software. It has an intuitive interface that allows beginners to become productive immediately and it contains the powerful drawing tools that font designers require to create and edit high-quality TrueType and OpenType fonts.
Apple macOS / Mac OS X software - convert svg to woff on OS X
Glyphs allows users to help draw new typefaces, modify existing fonts, and sculpt your letterforms hassle-free.
Multiplatform software - convert svg to woff on any platform
Birdfont is a free font editor which lets you create vector graphics and export TTF, EOT and SVG fonts.