How to arrange different scale drawings in one sheet?

By using layout tool you can do different scaling 

In AutouseCAD you can use only one scale for the sheet but inside this sheet if you want to draw in another scale you can do it by calculating and use the new scale for example your sheet scale is 1:100 then you will draw according to this scale while if you want to draw line inside this sheet in 1:50 scale then you have to draw the line of length 20 unit by 40 unit instead of 20 

process by the layout tool

YOU CAN USE SCALE COMMAND AS YOU NEED TO FIT SCALE TO WORKING IN SHEET

AS BUILT 1:100 IN NATURE

1:1000  IN MM INTERNATIONAL

SHOP DRAWING ALSO MUST BE IN METER

SCALE TO WHAT YOU NEED

JUST CLICK SC COMMAND YOU WILL FIND ALOT OF OPTIONS

The worst way to do that, is re scaling it in one sheet, for example enlarge dwg in 1/00 to 1/50 through double it! (scale factor=2) editing this tip of documents is awful! the best and easiest way is simply use layout and making view in that sheet. so you can apply different tip of scale in one sheet, arrange your sheet, modify your document in model place without any trouble. you should apply various tip of dimension and text style according the scale of your drawings in this method to avoid having different size of dimension and texts in print .

I think you are refering to a cut out/detail to show an enlargement of an item .... there been given many good answers abvove therefore no need to add any thing else

For arranging different scale drawings in one sheet use layout  tool ,in layout you can arrange different scales & arrange different drawing in one sheet.

The easiest way to do this is to first of all, choose the drawing that you'll want as the largest. When you start with the drawings that are smaller in scale, you can either draw them normal-sized and then re-scale, or you can draw them from the start with smaller dimensions (e.g 1:200 or the half).

This way, when you print out your work to scale, if it's 1:100 then the smaller one will be 1:200. And if you chose the scale as 1:50, then the smaller one will be 1:100.

The things that you'll have to know for this procedure are:

1- The difference between scales.

2- How to use the "scale" command accordingly.