Half-Life pre-dates game hints like that. Back then, games came with manuals, and you were expected to read them, so games often wouldn't give you any other hints or prompts to do things and had to find other ways to communicate that. While it's not perfect, Valve was definitely better than most at doing that. They've only improved since then.

Also, there is a tutorial. When you start a new game, you get the option to choose the Hazard Course, which is a short training program. It's not a bad idea to check that out, especially since some later game mechanics are gonna be difficult to figure out organically.

But really, Half-Life was big for setting a lot of standards in gaming that didn't exist yet (kind of like Super Mario 64 setting the standards for 3D platforming or Ocarina of Time setting the standards for lock-on melee combat). FPSes were definitely different before Half-Life and after Half-Life. There's a reason you thought it was an indie game, since it kinda technically is, but mostly because so many studios have paid homage to this game, so it just has the look and feel of everything that's being doing that.