This is a very difficult modal verb for Spanish speakers, as it’s very hard to directly translate it into Spanish.  But in English, it’s sometimes necessary.

Some of you will undoubtedly already know this verb for its use for the future for the first person

I shall go to the shops after lunch
We shall see

Oftentimes, however, this modal verb is abbreviated, and its abbreviation is the same as for “will”

I’ll go tomorrow (could be “will” or “shall”).

Indeed, in American English, shall is almost never used in this circumstance.

Where “shall” is still used is in making requests:

Shall I open the window?

Shall I get you a glass of water?

Shall we dance?

In all these cases, Spanish would just use the present simple, but English requires “shall”.

Here, shall is being used to express that the speaker would like to do the action and they are politely asking the other person if they want to take part.

It’s also used in questions tags to make a suggestion:

Let’s see the new Julia Roberts movie, shall we?