The_Gekko_State I am just very curious about this OSR thing. Mostly as the rules are all before my time and interested in how they are and what stories they make.
OSR is my jam.
Basically, OSR D&D is very similar to current D&D, but some of the rules will be different. Like, for instance, AC starts high and goes lower as it gets better; to hit rolls are made by cross-referencing a lookup table or doing a quick THAC0 (To Hit Armor Class 0) calculation. Not all races can be all classes, and sometimes races are classes.
The playstyle is what makes it the most different. There aren't as many codified rules, specifically relating to character capabilities; feats and skills generally don't exist. It relies on DM adjudication of the existing rules to allow for the things that feats and skills cover today; "rulings, not rules" is a common saying. Also, it's more descriptive and narrative. For instance, this generally won't happen in an OSR game:
"I search the room for secret doors. I rolled a 15 on my d20, plus 2 from wisdom, and plus two because I'm proficient, for a total of 19."
"You find one behind the bookcase."
Instead, it will be something like this:
"Hmm, what's in the room?"
"There's a bed in one corner, old, with tattered sheets. It doesn't look slept in for years. There's a dusty bookcase in the other corner."
"I'm going to check out the bookcase. Is there anything on it? I'll look behind it too."
(DM rolls 1d6, as they've determined that anyone checking behind the bookcase will find it on a 1, 2, or 3; they roll a 2)
"As you slide the bookcase back, you discover a small door that it was hiding."
So yeah, let me know if you have questions or anything. I can talk about this stuff for hours.