The following are the base vowels that have long pronunciation (The dashes are there as place holder for a consonant)

-า (a)

It makes "a" sound like in English, as in "baah", "barn", "yarn", etc. It goes to the right of the consonant.

-ี (ee)

It makes "ee" sound like in English, as in "bee", "meet", "see", etc. It goes on top of the consonant.

-ู (oo)

It makes "oo" sound like in English, as in "boo", "zoo", "moon", etc. It goes below the consonant.

เ- (a)

It makes "a" sound like in English but different from -า, it is the "a" as in "say", "pay", "may", etc. It goes in front (to the left) of the consonant.

แ- (a)

This one also makes "a" sound like in English but different from -า and เ-, it is the "a" as in "sad", "mad", "map", etc. It goes in front (to the left) of the consonant.

โ- (o)

This one also makes "o" sound like in English, it is the "o" as in "so", "mow", "dough", etc. It goes in front (to the left) of the consonant.