There are situations where both simple and continuous forms can be used to express the same idea. For example, both sentences given below express the same idea.

• How long will you stay in Germany? (Simple future)
• How long will you be staying in Germany? (Future continuous)

If someone asked you that question, you could, for example, say two weeks, ten days or one month.

Now consider another example.

• ‘Where do you work?’ ‘I work in Beijing.’
• ‘Where are you working?’ ‘I am working in Beijing.’

These sentences, too, express more or less the same idea. However, there is a little difference between these forms. A native speaker is more likely to ask ‘How long will you be staying in Germany?’ if he / she suspects that your stay in Germany is likely to be temporary. If you were a German citizen, they are unlikely to ask that question in the first place.

Continuous forms are mainly used to talk about temporary situations that started sometime in the past, and is still continuing. Simple tenses, on the other hand, are used to talk about more long-lasting or permanent situations. The simple tenses are also used to talk about things that happen all the time or things that are always true.

If you ask someone where they live / work, you probably expect them to live / work there for a long time. On the other hand, if you ask someone where they are working / living, you probably suspect that they will move into another office / place sometime in the future. That said, these differences are relatively insignificant. Even if you use simple tenses to talk about temporary situations, you will still be understood.