I am just uploading a text to amazon publish and it is asking me for a trim size, can someone please tell me what is the trim size used in texmaker because I want to keep my page lining etc. Thanks.
I know nothing about texmaker, but this is a possible scenario.
Think of your typical inkjet or laser printer and the paper that you print on, typically letterpaper or A4. Call this the stock size (or papersize in LaTeX terms). You print your text on this and it is positioned relative to the size of the stock. You send your book to the publisher and they might not use the same stock size when they do the actual printing (they might quite possibly print several pages at a time on a large sheet of paper which is then cut into individual pages). Come binding time they want to know the what the physical dimensions of the sheets as published in the book should be. Often when a book is bound the edges of the sheets are not smooth, a little ragged. These rough edges are then trimmed to make the book block edges tidy. That is the trimmed size.
Roughly speaking, the trimmed size is what you want the final book block size to be.
layouts package and the
memoir class have illustrations of this.
I suppose that the question revolves around how you want your published book to look. An A4 or letterpaper sized book is somewhat larger than usual. Please consider the final output, not what you get on your home printer.
PS. I have been a (traditional letterpress and LaTex) printer and bookbinder and there are many things to be considered when hoping to get a book published, and more importantly purchased.