Suppose , i have a paid host...which offers me 5GB webspace.. and 250 GB badwidth etc. now , since the space is too much for me , and i want to use the space for 2 websites.. suppose i have 2 domains , domain1 and domain 2 .. is it possible that i host both of domains there ? domain1.com will be totally different website and having different files..and domain2.com will be different. i mean , can i make 2 different websites on one hosting space ?? i hope my question is understandable..
if it is possible , can some one tell some hosts names which allows this ??

well it is possible..but it will be just a work around.
You can create a new subdomain and then forward the second domain to this subdomain. This way your site will be hosted on the same space.

This is the way I know..may be someone else..has another way of doing it.

For me, I'm using free subdomains. Hence I'm required to enter a URL in the subdomain configurations for it to point to. I host 2 websites, hence I entered 2 different URLs to the subdomain configuration. Both actually pointing to the same webhost, but different HTML file. This is another way of working. This way, you can have alot more sites hosted on your same webhost account with individual domains for each of them.

Yes you can have more than one domain, almost every paid hosting allow multiple domains, you just have to create on your Cpanel another domain (usually the name is "Addon Domain") then a folder will be automatic created with the name of your domain, so the web files of your new website go in there!
Point your nameservers of your domain to your hosting, wait several hours to changes take effect and that's it!

Stay well.

Though most of the hosts do not reveal this, it is true that they support multiple domain hosting on a single account.
What you need to know:
1- Create a folder parallel to your existing domain folder on the hosted space.
2-Rename it in the 2nd domain name and put a index.html file there.
Now try to access the address(2nt domain) from browser. If successful(very probably), You are done.