Step 1: Understand what language learning needs:
A language is learnt by taking in the language and by using it.
So the skills are of two kinds. Two skills are used to receive a message, and two are used to give a message.
Step 2: Name the four key skills:
1. Listening
2. Speaking
3. Reading
4. Writing
Step 3: Explain each skill:
Listening: understanding what others say. It is the first skill a child gains.
Speaking: expressing ideas clearly in spoken words.
Reading: understanding printed or written text and picking up new words.
Writing: putting thoughts on paper in correct grammar, spelling and style.
Step 4: Group them:
Listening and reading are receptive skills, because we receive the message.
Speaking and writing are productive skills, because we produce the message.
Final Answer:
The four key skills for learning a language are listening, speaking, reading and writing.