Hello there,
as it has been said, you asked a very broad question and this is usually covered in large manuals, instead of a mere message on a board.
Let's say, first of all, that Cisco is very good in documenting things and each hardware product (at least those I have been working with) has an hardware installation guide, which I suggest, you should read.
Where to find it?
type http://www.cisco.com/univercd the product documentation page will show up. Let's say you have a 2600 to install so you choose the router drop down box and the the modular router item (sorry but you need to know what kind of equipment you are working with). This asction will bring you to the following URL:
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_mod/index.htm
Here you select the router series you want (we said 2600) and on the resulting page you select the Hardware installation documents, on the next page you select the hardware installation guide and then the first link is the whole guide in .pdf format. The link you should end up with is:
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_mod/cis2600/hw_inst/2600hig/2600hig.pdf
I suggest you read this through since it explains alot wich is applicable to lots of other routers. Since this is a modular config router it will explain network module and wan interface card installation too. This is a 120 pages document which I cannot sintetize in a post.
I hope this is what you are looking for and there should be one for you specific hardware type.
Fabio
