A layout is a 2D environment where you can specify the size of your drawing sheet, add a title block, display multiple views of your model, and create dimensions and notes for your drawing.
There are two distinct working environments in which you can create objects in a drawing - Model space and layout space.
Typically, a model composed of geometric objects is created in a three-dimensional space called model space. A layout of specific views and annotations of this model is created in a two-dimensional space called paper space.
Paper space is a sheet layout environment where you can specify the size of your sheet, add a title block, display multiple views of your model, and create dimensions and notes for your drawing. You can use multiple layouts to show and provide details on the various components of your model. You can vary the scale of the model view to show small details which are part of a bigger three-dimensional model, on standard-sized drawing sheets.
The two spaces are accessible near the left bottom corner of the drawing area: the Model tab and Layout1 and Layout2 tabs.
You can add new layouts or copy existing layouts. You can create layouts using the Create Layout wizard or DesignCenter. Each layout can contain different page setup settings.
On each layout, you can create as many layout viewports as you like. Each layout viewport is like a picture frame into model space, containing a view that displays the model at the scale and orientation that you specify. You can create a single layout viewport that fits the entire layout or create multiple layout viewports. Once you create a viewport, you can change its size, properties, and also scale and move it as needed. You can also specify which layers are visible in each layout viewport.