From my point of view.

What is the example of giving opinion in the formal way. If you ask me I would have to say that opinion. Giving an opinion is a common way of interacting with other people in formal and informal settings. I dont think I care of it.

In my opinion. To be honest In my honest opinion. Formal expressions are used in a situation where you are talking in a formal situation such as in the office or school between the teacher and students.

As far as Im concerned. In academic writing and other formal types of writing such as professional reports it is usual to give your opinion implicitly. I hold the opinion.

For the former you could give them an activity where lots of examples are compulsory or necessary and tell them to use different phrases each time. Asking and giving opinion. If youre conversing with an authority figure its probably better to let them ask for your opinion.

An introduction where the topic and the authors opinion. I dont think much of it. You might need to state your opinion in speaking or writing.

You need to use an appropriate expression to asking or giving opinions. Informal expression are used in a situation where you are talking between friends or close. Learning English has become a must.