Changes

The first line seems to order ConTeXt to "install" (for the current file) the given typescript (it accepts what I have earlier called a "typescript name"). The last one starts using it (you may omit the size if you are satisfied with the default).

It is also possible to combine fonts from the TeX Gyre collection in your own typescripts. The example below combines Bonum (Bookman) roman, Adventor (AvantGarde) for sans serif, Cursor (Courier) for teletype, and Euler for math. The <code>rscale=...</code> option ensures that all fonts have the same x-height. (You can lookup the relative x-heigt of a font using fontforge.)