How do I adjust margins on a writer document; how do I find the tool to address and envelope

I am new to LibreOffice. I am finding it very frustrating to find out how to adjust the margins on a word-processing document (letter, etc.) and to find the tool for addressing envelopes.

To adjust the page margins of a document go Format (menu) > Page. . . > Page (tab) There you will see the margins you can set.

Don’t know how to deal with your addressing envelopes issues. However, there is a item Insert (menu) > Envelope… which probably offers what you are looking for. I’ve never used it so can’t comment on how to.

You might find the following two books useful:

LibreOffice 5.1 Getting Started

Designing with LibreOffice

Both books are free unless you want a hard-copy.