Particles are quite important for displaying the mood of the sentence or whether it is a question or a statement. There are quite a few and to be honest when I’ve heard different ones used and read the definitions I’m not convinced that people use all of them, or in fact differentiate so much between them.
A comprehensive list can be found at CantoDict and I have summarised the main ones that I use and have heard being used below.
Used to end questions. The question still exists without the particle, but it’s a way of softening the abruptness of the question, like when people raise the tone at the end of question in English.
nei5 zou6 mat1 je5 aa3
What are you doing?
Used in the same way as 呀 but for statements. It’s used a lot by “MK” boys / girls who 喇 almost everything – something which has to be avoided when learning! One of my first teachers added 喇 to everything and it makes you sound like a tool when you’re talking to everyday people in shops and bars. Only use it when you need to soften a sentence – like if you’re saying “oh, it doesn’t matter”, that kind of statement could sound abrupt. Adding 喇 makes it more casual.
This is a question particle. To be honest I have only really heard it used apart from in the example question but I’ve used it interchangeably with 呀 and it doesn’t seem to cause people to say that I’m wrong. Edit: I heard this particle used a lot in a conversation between one of my co-workers and a security guard who was claiming we were trespassing. My co-worker was basically trying to make light of the situation but was using 嗎 instead of 喇。
nei5 hou2 maa3
How are you?
Again, I haven’t heard this used very often, but according to CantoDict it’s to imply that information is being reported, and that the listener (when pronounced wo5) may not agree with it. I’ve only ever heard it used when I’ve asked a question and the person has replied “唔知喎” (m4 zi1 wo3), which means “I don’t know”. I guess, in a sense, this does follow with the above definition, and if I listened harder I would probably hear it come up in other sentences, it’s just that in 唔知喎 the 喎 is usually exaggerated.
There are a lot more particles than just these, and it is worth having a look through them and trying to use them in the correct situations. You can get away with not using them, but I’d say 呀 and 喇 are quite important.
Recently I’ve also seen people write 吧 (baa1) which is basically a way of stating a rhetorical question. I thought it was a typo and replied anyway – the simplest of miss understandings.