"The little boy wants to study."
Translation:Cậu bé muốn học.
Basically, they change the way you tone your voice. There is a way to pronounce each one. I will give an example with one single word (Ghost). Ma - "Ghost"; say at a steady tone at the middle or top of your voice. Má - "Mom/mum"; start at center of voice, and go towards the top of your voice at the end of the word. Mà - "But"; start at center of voice, and go towards the bottom of your voice at the end of the word. Mả - "Tomb"; start at center-bottom of voice, dip down slightly, and go back up higher (or at least I think). Mã - "Cypher"; start at center of voice, dip down slightly, glottal stop (look it up), and go back up. Mạ - "Can mean mom/mum", but also means seed; steady tone at the bottom of your voice.
Also, there are more characters, but those are to change the actual pronunciation (from what I've learned over the past year with two different Vietnamese friends) rather than the tone of which you say the words.
Like the karat, which appears over this a: â. This just changes... something. I don't know, what exactly, it is supposed to do. There is also an inverted circumflex: ă, which makes it a more back-of-the-throat vowel. There is, lastly, the...thing.. I forgot the name, but it's the.. hook, I think? The letter u changes to ư. It makes the same "oo" noise in the word "book."
I hope that this somewhat helped, even though it adds about twelve new letters to your vocabulary.
It is also in the next lesson.
They are called diacritic marks. I took VN lessons for a month or so before going to Vietnam in 2015. My tutor called this one "~" creaky lol.
Others are right about the necessity of having the tonal pronunciations to make these lessons more complete. While the grammar and vocabulary started coming together for me when I was first starting, when I actually got to VN and tried conversing I just butchered most pronunciations :)