My correction is in Cantonese not Chinese.

先日記 - 你好 我叫 Matt

你好. 我叫 Matt. 我寫 從來沒有未寫過中文字.大部份都係從字典揾出來. 我唔自乎在寫但纔我知很多 我用字典 我先專偈廣東話 要曉講然後學寫.

Literal translation so that you can learn easily.

I hope that is readable. 

希望寫得明白(清楚) Hope that what I had written is understandable (clear)

That is the first time I have ever tried to use the symbols,

今次係我首次寫中文字 This time is my first to write Chinese characters.

mainly using a dictionary.

大部份都係從字典揾出來 The majority came from the dictionary.

I first want to focus on speaking, 

首先，我要專注於點講 Firstly, I want to focus on how to speak

then later learn to write.

然後學寫.

However, we don't speak like this in Cantonese.  It would be 我先要曉講然後學寫. Learn to speak first and then learn how to write later.

希望大家能看懂。

你好 !我叫 Matt。這是我第一次寫中文,所以當中大部分是用字典翻譯的。

 
I hope that is readable. That is the first time I have ever tried to use the symbols, mainly using a dictionary. I first want to focus on speaking, then later learn to write.