Pathfinder can be a bit overwhelming to new players due to the sheer, massive volume of rules involved. The learning curve isn't nearly as steep as it might appear, however, because a player really only has to know a tiny slice of those rules. If you're a fighter, for example, you don't really need to know that much about the mechanics of the multitude of spells that a wizard might be able to cast. Conversely, if you're a wizard, you don't need to know that much about the intricate mechanics of melee combat. I'd recommend reading the section of the D&D 5th edition basic rules that GenKitty cites that describes how gameplay actually works in practice, while disregarding (for now) the details of combat and spell casting mechanics. That will give you a feel for how the flow of the game actually works. you may also wish to spend a bit of time on youtube or on twitch watching streams of actual Pathfinder or D&D games to see how gameplay actually works. Pathfinder and D&D are often mentioned together because Pathfinder (for legal/business reasons) is a variant of version 3.5 of the D&D rules. D&D has produced two versions of its rules since Pathfinder's "fork in the road," the fourth edition (which is generally regarded as a flop) and, within the past year, the fifth edition, which has much more favorable reviews. Although the details of the rules differ, all of them (Pathfinder, D&D 3.5, 4.0 and 5.0) operate in similar fashion, so if you know any one of them, picking up the others is very straightforward.
