I'm watching '2001: A Space Odyssey' (1968) for the first time!

The Monoliths are are tools of advanced aliens. They can perform tasks such as give the alpha hominid the idea of using the bone as a tool/weapon. One is later buried on the moon to act as an alarm to let the aliens know we've achieved space travel. The one near Jupiter acts as a Stargate to another galaxy.

I think of Kubrick's film as a painting. It doesn't tell the whole story because Kubrick was telling it mostly through imagery. Clarke's book helps spell out the details. As I recall, it's a quick and easy read. Each chapter is only a couple of pages long. After reading the book I watched the film again and it made a difference.

2010 is more of a traditional film which tells the story. I second Anthony's suggestion that you watch it next. HAL is also in it.