These sounds can be confusing, because about 150 words are spelled the same in UK and US English, but are pronounced differently. For example, "path," "chance," and "example" are pronounced with /a/ in the UK and /ae/ in the US.
On the other hand, a single "o" is usually pronounced /a/ in the US. For example, words such as "shopping," "hot," and "clock" are pronounced with /a/ sound.
Please listen and practice the sounds and sentences on the podcast. The tongue twister is something I simply made up on my own...maybe you'll find it easy, maybe difficult. Give it a try!