When's the right time to use 這麼 and 那麼 in Mandarin?

咁大=這麼大
係咁=那麼

這 = this / these (near)
那 = that / those (far away)

這麼 (near), 那麼 (far away) = so


*In additional, we say "廣州話" and we don't say "廣東話" because all people in Guangzhou say "廣州話".

這麼　= used for referring to things or topics close to you, or something/someone that's present.

那麼 = used for referring to things that are further away or you are talking about something/someone that's not present.

Conditionals:
這麼 = then this (is .... )
那麼 = then that (is .... )

咁 in Cantonese = 這麼 in Mandarin.

"We speak Cantonese in Hong Kong":
1. 我們在香港都說“廣東話”
2. (我哋喺香港講"廣東話").
1. & 2. mean the same: 1. is in Mandarin, 2. is in Cantonese

"In additional, we say "廣州話" and we don't say "廣東話" because all people in Guangzhou say "廣州話"."
People in Hong Kong DO say "廣東話" & the occasional "廣府話" when referring to the Cantonese used in Hong Kong. 廣州話 is only used in Hong Kong when referring to the Cantonese used in Guangzhou, China, which might have some different vocabulary due to the influence of putonghua in Cantonese, where putonghua is the official language in China, but Cantonese is one of the official languages in Hong Kong besides English. Some Cantonese words used in Hong Kong have English origins. Some Hong Kongers can't speak perfect Cantonese.

Hi hi,

這麼 and 那麼 means 'so' in certain usage.

Eg, why are you so naughty? Both can be use in this case.

這 pronouse as 'zhe' may means here, this, or now.

那 pronouse as 'na' may means there or that, be it time or place.

麼 read as 'mo', when join with other word will change the words/phase into question form, or to emphasis something.

The best thing is, get a chinese speaker to give you a few more example, and you will see how to use it. I can type to you, but you may not pick up the right tone.

Cheers