Hola John
The form "yendo" in Spanish is the gerund form of "ir" (going) so you will find it in progressive tenses for example:
Estás yendo muy rápido.
You are going very fast.
Or you could see it when saying "by going..." or "while going...", for example:
Aprendes mucho inglés yendo de vacaciones a Inglaterra.
You learn a lot of English by going on holiday to England.
Yendo al supermercado vi a Marcos.
While I was going (=walking) to the supermarket I saw Marcos.
Saludos
Inma
