I always use simple words to describe my thoughts

I chatted with my friend yesterday, and I told her that I had found a great website called "italki", where I can writeing something in English and many people will help me by giving me feedback. , but However, she told me if I want to get be better, then I must know lots of many words.  ,and She also said that, "the more words in your memory, know, the more you can understand always know what are they are talking about." I think she is correct, but to remember all these words is difficult to for me. , I used to study memorize words from the dictionary starting from A, Abandon,......., but actually I can't remember more and more , still less till Z. Even before I am finished with the A-words, I had forgotten most of them because most words I never use them usual in my daily life time.

Although I am always writing using simple words in my writing, it is time to start learning more difficult words here is my way to restart now.

Bee's advice is excellent.  You should listen to him.  It is the same in learning Chinese characters.  Simple characters can only convey simple thoughts.

I always use simple words to describe my thoughts

I chatted with my friend yesterday, and I told her that I found a great website called "italki", where I can writeing something in English and many people help me by giving me feedback., bBut she told me if I want to get better, I must know lots of words, and she also said that "more words in your memory means, you can always know what are they talking about." I think she is correct, but to remember words is difficult to me., I used to study the dictionary from A, Abandon,......., but actually I can't remember so many wordsmore and more, still less totill Z. Bbecause most words I neverwon't use them usual in my life time.
Although I am always writing simple words, here is my way to restart now.

Nice job!  I disagree a little bit with your friend because most words are not commonly used, as you say.  You can look up unfamiliar words that people write or say to you, and also look up words that you want to use.  Then work hard to memorize those words.  As you use more English, you will gather more and more words to memorize.  In this way, you will be working on words that you actually use, and your vocabulary will improve the more you use English :)