hi !
Nous mangeons un sandwich en ville
Manger (infinitive)
you have to add a "e" before "o" to have the sound as "jo/in' otherwise you'll have a sound as "go"
je mange
tu manges
il/elle/on mange
nous mangeons
vous mangez
ils/elles mangent
same when you'll have to conjugate at the "imparfait"
je mangeais
tu mangeais
il mangeait
nous mangions
vous mangiez
ils mangeaient
so before the vowels "a" and "o" , you have to add an "e" to get the sound "je" as "join'...otherwise you get an improper sound as "go"
Not sure my explanations are very understandable, but I tried !!!
have a nice day !!