Here's a "how-to" on jzIntv, the most accurate and supported Intellivision emulator.
https://www.reddit.com/r/intellivision/comments/4etfy4/howto_use_jzintv_emulator_the_easy_way/
Unless you're using an Intellivision controller, it's helpfull to have a button mapping specific to certain games. You can do this with jzIntv and Launchbox.