There are six simple finals in Mandarin: "a", "o", "e", "i", "u", "ü".

The pronunciation of "a" is like the sound of "a" in the English word "car" and the sound ofthe Cantonese word "阿" (aa1, prefix used before monosyllabic names).

"e" is close to the "o" in Mandarin, except the mouth is unrounded. It is close to the "uh" sound in English, like the "e" in the word "her" and "the", but there is no equivalent of the Mandarin "e" sound in Cantonese.
"i" in Mandarin is similar to the sound of "ee" in the English word "pee" and the final of the Cantonese word "衣"(ji1, clothes).
"u" in Mandarin is like the English "oo" in the word "boot" and the final of the Cantonese word "烏" (wu1, black)
"ü" sound is like the final of the Cantonese word "於" (jyu1, at), but there is no equivalent in English.