Domain forwarding question!

Hi - I have a few domains with keywords that heavily relate to my main website.

Can anyone tell me - what is the best way to use them when they're being forwarded to my main site? Do search engines pick up and rate the content they point towards or will they just see a blank site linked to another?

I hope this makes sense and thanks!

Actually, inter-linking of your own websites isn't a great idea; Google doesn't like this as it's manipulation of search results, and can result in a penalty.

You can 301 redirect the domains to your main domain and build links towards the 301 redirected domain. Since your 301 redirecting those links and their value are passed on to your current domain name.