First of all, it will have to be made clear that there are variations in the subject matter in the standard British English grammar and in American English. Therefore, the participants in the discussion may not quibble about what is correct and what is not. Generally, in India, people are taught British English grammar in their school days. However, in the present internet era, the boundaries have melted and in future, only very recalcitrant individuals will heckle about such issues.
Will is primarily used when talking about the future e.g.
1. When will you go to Delhi?
2. Hopefully, we will have a good monsoon this year.
Its negative form 'will not' is shortened as won't e.g.
1. They won't be able to scale the mountain.
2. iPhone7 won't be available till next few months.
However, while talking about the future 'will' is generally used with second and third person pronouns viz. you, he, she, it, they) etc. With first person pronouns i.e. I and we, the convention is to use 'shall'. In spoken English, 'will' is generally used with the first person pronouns also in shortened form e.g. we'll.
The trend is that that these two verbs are generally interchangeable in most, but not all, situations.
Let us encourage each other in sharing knowledge.