If i want to say demo (demonstration) can i use both shi4 fan4 and yan3 shi4?
Like for demo class - shi4 fan4 ke4 / yan3 shi4 ke4
2 - If i want to tell some one to turn around, like they facing away from me - then can i say - xuan2 zhuan3 yi xia4
3 - How to say - Please pour me a cup of tea?
3. How to say - Please pour me a cup of tea?
1.Yes, the demo class you can say:shi4 fan4 ke4 / yan3 shi4 ke4
2. If you want to tell some one to turn around, you can say: zhuan3 shen1.
3.Please pour me a cup of tea: qing3 dao4 yi1 bei1 ka1 fei1 gei3 wo3
You can read above as reference.
Hope my answer can help you.
1.I think 示范课（shì fàn kè ） is better than 演示课（yǎn shì kè ）.In our daily life，we said 示范课（shì fàn kè ） more .Actually I never said 演示课（yǎn shì kè ） to describe (demonstration) in my daily lifeBut you can use both of them. The meanings are very similar.
① 示（show）范 （model，exemplar)（shì fàn ）：a model example
②演（to act，perform）示（show）（yǎn shì ）： to show
3.能给我倒杯茶吗？（néng gěi wǒ dào bēi chá ma ？） pour means 倒（dào ）
Okay，Jason.Do you need some chocolate at the time？You like chocolate so much.haha
Whether I solved your questions？If you are still confused ，you can ask me face to face oh.