DOOM on-line help

From this page you can install all the DOOM levels 
we've provided by pressing (believe it or not) the 
'install all levels' button. This will need about 
5MB of space on your hard drive. If you pick this
option and the program asks you whether or not to 
'overwrite' a file press 'y'. Don't worry this is a normal
procedure. 

To install an individual DOOM level click on the appropriate
button and you will be able to choose a directory 
(by default C:\DOOM) to install to. Once the new level has been
installed you can play it by exiting from the CD and
changing to your DOOM directory (with any luck the
same directory that you installed the new level to).

Type: DOOM -FILE NEW_WAD_FILE.WAD <RETURN>

where NEW_WAD_FILE.WAD is the name of the new level
that you've installed.

Some of the levels come with their own batch files that
do the job for you.

I would recommend that you read the text file before 
installing as this provides useful information such as the 
number of the level which you have installed. You will 
need to know this so that you can 'jump' to it once you
have loaded DOOM. To access the level, run DOOM 
(see above) and then type, for example, IDCLEV 1 3
This will 'jump' you to the third level of the first world.
Substitute the 1 and the 3 for the numbers supplied by the
read me.