How to set viewports in Autocad?

First step is to launch the command from the View Menu -> Viewports -> New viewports or from the Command Line: _vports.Once the Viewports window is open,you have to give it a name,then you have to choose from the menu how many viewports you want(Single,Two,Three,etc.,Vertical,Horizontal),set up it for 2D/3D,set a visual style(2D Wireframe,Realistic,Conceptual,etc.) and if you have named views(e.g Custom Views created from the View Menu -> Named Views),you can choose one of this views for your viewport configuration.

Dear lvan,
viewport command better to use in model space for proper layout of drawing.

Of course, using viewports generally means you have a layout setup with a title block, etc. Thus if you have a drawing in your model space that you want to display on your title block, the only way to get it there is using a viewport.
So, go to your layout, click on your viewport icon surround your drawing to be displayed. There's a lot to know about it to get proper scale for any given sheet size and scale setting. If you need a title block with scales and dimension styles already set up, let me know, and I'll send you a great one I inherited and have been using and adding to for years. :) Note: you can also convert a polyline or any shape to a viewport. Very handy if you have limited paper space and don't want to overlap anything.