The Real Difference Between "shall" And "will"...

There are certain 'rules' in standard British English grammar regarding the distinction between 'will' and 'shall' which you should be aware of, even if the current consensus is that these two verbs are generally interchangeable in most, but not all, situations.

In British English, there has been a traditional rule of prescriptive grammar stating that, when expressing pure futurity (without any additional meaning such as desire or command), shall is to be used when the subject is in the first person (I or we), and will in other cases.

Forming the Future Tense with 'Will' in 'Shall' (Traditional Rules)
The traditional rules for forming the future tense with will and shall are:
Person Pronoun Noun Future Tense Example

1st Person Singular I shall -> I shall be there soon.
2nd Person Singular You will -> You will be there soon.
3rd Person Singular He, She, It will -> He will be there soon.

1st Person Plural We shall -> We shall be there soon.
2nd Person Plural You will -> You will be there soon.
3rd Person Plural They will -> They will be there soon.

Although it's okay to use will in every instance. But during exams, it's advisable to stick to the rule. Unfortunately, this topic doesn't end there.

Conveying a Sense of Importance or Duty with 'Will' and 'Shall'

If something is to happen in the future and you want to convey the idea that it must definitely happen (especially out of a sense of duty), then it all switches. In other words, it goes like this:

Person Pronoun Noun Future Tense -> Example

1st Person Singular I will -> I will attend the meeting.
2nd Person Singular You shall -> You shall attend the meeting.
3rd Person Singular He,She,It shall -> He shall attend the meeting.

1st Person Plural We will -> We will attend the meeting.
2nd Person Plural You shall -> You shall attend the meeting.
3rd Person Plural They shall -> They shall attend the meeting.

'Shall' Is Still Used in Questions

From what you've read so far, you might be getting the idea that shall is on its last legs as a word. However, that's not accurate. Shall is alive and well when it comes to questions posed in the first person (i.e., with I and we). For example:

Shall I talk in a Yoruba accent during the meeting?
What shall we talk about?Was that the dog?
Shall I open the window?

'Will' and 'Shall' in Contractions

When talking or writing informally, you might not have to worry about whether to use shall or will because the contractions are likely to be the same. Here they are:

Full Versions Contraction

I shall, I will -> I'll
You shall, You will -> You'll
He/She/It shall, He/She/It will -> He'll / She'll / It'll
We shall, We will -> We'll
You shall, You will-> You'll
They shall, They will -> They'll

This overlap does not occur with will not and shall not (the negative versions).The contraction for shall not is shan't. The contraction for will not is won't.