Platforms that I use for Q&A purpose

Due to the power of the Internet, people can exchange their knowledge to each other around the world just in a second. However, I see that many students, especially in Vietnam, lack this skillset because they may not know there are many free sources on the Internet which allow them to discuss with other people about what they want to know. That's why they need to pay money for going to tutorials every single week. Honestly, I didn't know there are many free mind-sharing sources on the Internet when I was studying in Vietnam.  Therefore, I'm going to share some free mind-sharing sources I'm using for study and work in this post.