I am trying to get the red key on PC in Doom 2 second level. But, I can see the key but can't figure out how to get to it. I played this game 25 years ago on a dinosaur computer but now on my laptop I can't seem to find how to get the key. Im Probly just old like my old dinosaur computer but any help would help. Thanks!

Those levels are arranged/labelled in a funny way. Do you have the name of the level?

All I know is I passed the first level and was on the second. Looked like there were some stairs leading to the red key but I couldn't get to the stairs because a wall was blocking.

You could look at the map, the level name is usually written there.

Sounds like Underhalls, if it is then it's just a matter of running/sprinting into the building the key card is in. You can see it done in this video - https://www.youtube.com/watch?v=h-nHoy3gWpY

If it's not Underhalls and is in fact a Master Levels map, if you can figure out which one it is, then you might look here for the corresponding map name and read their walkthrough.

Next time please hit "tab" and read the level name, check the corresponding .wad file and search the Google/YouTube.
https://www.youtube.com/watch?v=9LYlIzumiXE

Interestingly, the level names seen when you hit TAB can be different from the list. E.g. *Bloodsea' is 'Dead Simple' (or something similar) when you read the map.

'Blacktower' is a fantastic level btw. One of my all time faves.

TheMonkofDestiny is right, it would be 'The Underhalls'. The Master Levels are not arranged in a megawad, but single wads that you have to activate one by one. When you finish any Master Level, you will be taken to the second level of the original Doom 2 campaign, which is The Underhalls.

To get to that red key you walk around to the side of the brown building and, as TheMonkofDestiny suggests, jump across to the opening. It's an easy jump. But you might as well skip it (ha ha) altogether since 'The Underhalls' is not a Master Level.

Thanks so much!