shell = раковина, снаряд, скорлупа. she'll = abbreviation of "she will". The word I think you were looking for is "shall", which is a word of similar meaning to "will". In modern English we do still use shall, but it's definitely less common than will. It tends to be used more in written language rather than when we speak. The only time I would say I definitely use it is when I'm asking for confirmation to do something, specifically when I want permission/affirmation to do something: "Shall I call him?" "Shall I bring your things this evening?" In this context, 'will' carries too much authority so we use shall. But don't worry about it, they're more or less interchangeable. :)

Yes, we still use "shall" in modern English, and you should definitely know how and when to use it. There seems to be a funny myth going around Russian teachers of English, which says we don't use it anymore. Silly.

в выражениях типа "Shall I open the window?"

Both are correct, I guess. "She'll" is a contracted form of "she will" ;)

ShAll