Firstly receiving spam is nothing to do with Outlook (or any viruses / malware on your computer), it is because your email address has found it's way onto the spammers list which unfortunately it is a fact of life - if you have an email address you will get spam. However sensible precautions about who you give your email address to and which websites you type it into can minimise it.
You can block specific addresses within Outlook, if you right click on an email, scroll down to "Junk" and then select "Block sender". Of course this only blocks the specific address that particular email came from and the spammers often use many different addresses so you have to keep doing it. Often the simplest solution is to just delete it, and of course NEVER click on any links or attachments in the spam - not even links that might say "unsubscribe" etc. - clicking it just tells the spammers that your email address is valid and in use!