「これって英語でなんて言うの？」に英語のプロが回答する無料Q&Aサイトですって英語でなんて言うの？

Unless you are actually showing your friend the site while you are explaining it, then it may be better to use "it's" instead of "this is." For example, if I bought a new house and I want to show my friend, I would say "This is my new house!" as I am showing them a picture on my phone.

"This is" is also commonly used when introducing two strangers to each other. For example, if I want to introduce my friends Chris and Anna, who have never met each other, I would say "Chris, this is Anna. And Anna, this is Chris."

"Basically" is a natural term that natives use to explain a complex or extensive concept.

"English learners" are individuals who are learning English. Since I already indicated that these individuals are learning English, there is no need to repeat the word "English" and say "...ask questions about English..."

Therefore, "ask questions and have them (English questions) answered" is a good phrase to use I think.

"question and answer" describes the type of site it is.
"Native English speaker" someone whose first language is English.
"Translate" to change into English.
'Free' costs no money.

The term Q&A stands for 'questions and answers' so people ask questions and somoene answers them
a person that speaks a language as their native/mother tongue is called a 'native speaker' although you can also say 'English speaker'
When you are not charged money this is called 'free'

The best way to explain the site would be to physically show someone the site and talk them through the basic features. You could do this quite easily by using Skype screen share or a similar application.

"site" is short for website.
"native speakers" people who has spoken English from earliest childhood.
"post" means to submit

Free- It does not cost any money.
Native English speaker - Someone who uses English as a first language.

Uknow is a site where you can ask native English speakers to translate your questions for free.
It is a free site where you can get questions translated by native English speakers.

"A website in which native English speakers will answer any questions you may have about the English language."
This sentence is used to explain what the website DMM Eikaiwa Nante uKnow is about.
The term 'Native speaker' is used to describe someone who is born and raised with that particular language, in this case Native English speakers, so people from England,America,Australia,New Zealand etc.