The stress is on the first syllable. The 'g' is like the 'j' in 'Juice'. The 'e' is short as in 'gEt'. The second syllable is the unstressed schwa. (A very common sound in English.) This is pronounced like the second syllable of 'butter' or the second syllable of 'action'. The 's' is pronounced like a 'z'. If you look up 'gerund' in British English dictionaries online (Oxford, Cambridge, Macmillan), the audio will have a British accent saying the word.

Great answers.