Question : CNAME to point to Server in another domain

I have been asked to create a CNAME record to redirect a website to another host on a different domain.  I have included the instructions they sent me.  I would appreciate any help I can get with this.  I dont have a full understanding of how this works or how I would implement it.  Do I need an A record as well?  Please help:
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Step 1 (DONE). Choose a server name.  (You have chosen a server name in your domain - ir.foobar.com)

Step 2. You must ask your ISP to create a "CNAME" entry in the DNS table for that server name which points to the machine name of our IR Online web server: "123.foobar-ir.net".
NOTE: This CNAME entry must point to our machine name. The redirect will NOT work if pointing to an IP address.

Step 3. We will set up the redirect script on our server so that web browsers who come to our IR Online server from your server will be redirected to your IR Web site.

Once the above next steps have been completed, your IR Online site can be accessed at the server name you choose (http:// ir.foobar.com ), and that server name will mask ours on all pages within the IR Web site.  
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Answer : CNAME to point to Server in another domain

> Do I need an A record as well?  

No, you're pointing to the hosts A record which should already be in place.

That is, you should be able to do this already (if you replace the name with the real one, of course):

nslookup 123.foobar-ir.net

Your CNAME (Alias) points to that name. So you have:

ir.foobar.com   CNAME   123.foobar-ir.net

Does the help at all?

Chris