What is the difference between "先生せんせい（せんせい）" and "教師きょうし（きょうし）"
先生 is a title, like Sir, Mr, Mrs 先生, Dr, etc, and it means Professor, or Pro. It is added to the name：田中さん (Mr. Tanaka)；田中先生。(Pro. Suzuki)
It is the title for teachers and professors of all branches, including masters of martial arts. Being a title, you NEVER use it to refer to yourself.
Just like you never call yourself Sir, or Madame. You cannot call yourself "san", "sama", or "sensei".
On the other hand, 教師 is teacher or professor. When someone asks you what you do, you say: 教師です。 You never say 先生です。
(1) わたしは 高校教師です。
→ I am a high school teacher.
(2) こばやし先生に 日本語を ならいます。
→ I will learn Japanese from teacher Kobayashi.