They're all listed in the "Channel Store" (misnomer, most are free). Just browse
through by category (movies, news, sports, hobbies, etc), "install" the ones you're interested in, and check them out. If you don't like them, you can remove them.
Installing them basically means adding them to your channel list. But they have to be there to access them fully. Some actually take up a bit of memory depending on how complex the user interface is, so you are somewhat limited into how many channels & apps you can have active. But some models actually have a micro card slot to add memory if needed.
I'm currently running like 51 channels & apps with no sign of needing more memory. Most them I rarely use.
You'd probably like Crackle, they keep a bunch of older movies active, some newer, and even some original content. During your movies you will get an occasional commercial but only one at a time. They're on Roku just like Vudu, Pandora, & Spotify.But also like them, you can use their service straight from the internet if you don't mind viewing on your computer.
www.crackle.com It's free to sign up.
Another option is to have a laptop (like me) or decent video card that has an HDMI output. Then you can watch PC or Roku based movies on your TV.