Writing Cantonese is difficult not just for foreign learners but also for native speakers, because we have been taught to write standard Chinese, i.e. Mandarin, instead. There are many words that we don't even know how to write. Many Cantonese words did exist in ancient times but are now unknown to ordinary people. Basically nowadays we write Cantonese only in very informal situations, e.g. texting among friends. So, what do people do when they don't know how to write those words? They either create new characters or use characters that have the same or similar pronunciation. This results in a lot of inconsistency. For example, there are three ways to write "bei2" (give), namely 畀, 俾 and 比. 畀 is correct because it was used in ancient times, but it is less common than 俾, which is incorrect but pronounced the same. And those who don't know either of these two characters would write 比, which is simpler and has the same pronounciation. Therefore, natives speakers are very tolerant of such mistakes. We, except pedants, seldom criticise others for writing "incorrect" Canonese words. In fact, it is very common for native Cantonese speakers to mix Cantonese, Mandarin, English, abreviations and emojis in a single text message. So long as you can put yourself across, it's fine.

I think the style of written Cantonese among local people is more or less the same. However, when we type Cantonese on a computer, there may be some limitation, and it depends on the type of Chinese input method and the character database. People in the mainland may use Mandarin Chinese input method to type Cantonese ( as it is not convenient to install extra character database and Cantonese input method ). So, it is impossible to type the correct word sometimes, and using "same pronunciation substitution" is a common way to overcome this problem. For example, "好唔好" can be typed as "好吾好"，and it is still understandable. Usually, written Cantonese is quite flexible and it is acceptable to use substitution as long as the sentence is understandable. Of course, if possible, we should type the correct character :) Below is a link for your reference. It's an online Cantonese dictionary provided by the Chinese University of Hong Kong. https://humanum.arts.cuhk.edu.hk/Lexis/lexi-can/ .

The main stream input methods for Cantonese is Changjie which separate a Chinese character into different parts. For example: 明(understand) is separated into 日 and 月. However, it would be difficult for foreigners to use. There are two suggestions for you. 1. Using Cantonese Romanisation: not only easier to pick up, but also practice the pronunciation . 2. Skipping Chinese characters for spoken Cantonese: It is a common way for those foreigners who live in Hong Kong and can only speak Cantonese, as well as those foreigner-born Cantonese speakers. For example: 你覺得點？(What is your point of view) , you can type " Néi gok-dak dím".

Basically you can "write Cantonese" by typing characters with the same pronounciation. For example I type 佢地 They 好唔好 is it okay? 咁樣點算 if that's the case what should we do

The 就here means the same as Mandarin. .. you can read the Mandarin's book.