Showtime is a premium subscription network which means, in theory, that there is currently nowhere you can watch the channels unrestricted for free, unless you are in the US and have it as part of your cable subscription.
However, there are a few options available to you:
The Showtime website has some of the shows they have screened previously, available in full and for free. You'll have to be in the US to view them though, unless you have a VPN or something that blocks your location (a browser extension like Hola would help with that!)
Or you could check out this answer for help with how to view web content without country restrictions, and also for ideas about other sites that might have the TV shows you are looking for without having to go directly through Showtime.
