Ability scores can book of lairs for 5th edition pdf small bonuses to your dice rolls. Universal d20-based system of roll-over target numbers. EXP’s to advance to the next level.
Classes get features as they reach new class levels. Hit points, class-based hit dice. If a character has an ‘advantage’ for a skill roll or combat roll, the player rolls two d20 and takes the better one. If a character has a ‘disadvantage’, roll two d20 and take the worse one. Attributes are the same ol’ six, but more important than before. They’re used for skills checks and saving throws. Ability score increases are now class features, meaning that you have the potential to lose them if you multiclass.
Most classes get 5 ASIs, at levels 4, 8, 12, 16, and 19. Rogues get a couple extra, and Fighters get a couple more than Rogues. Feats are now fewer in number and more potent. If a character wants to obtain a Feat, they have to give up one of their Ability Score Increases to gain access to it.
There is a hard cap of 30, which cannot be exceeded by any means. DC 80 skill rolls, no more AC 120 monsters. Seems small, but see above about skill checks and ACs not getting stupid large even at high levels. Saving throws are like skills checks. Each class is proficient in two attributes for saving throws, so they get to add their proficiency bonus.
No more ‘fort’,’reflex’,’will’ per level, although Constitution, Dexterity, and Wisdom are still the three most common saves. Each class gets two saving throw proficiencies, one “common” and one “uncommon. Races come with racial bonuses, but some races also choose a racial sub-type. 2 Strength and medium armor training. This has been around since Dragon Magazine was still a print magazine, but it’s codified right there at character generation. The exceptions are humans, half-elves, half-orcs, and tieflings. It is very similar to 3e Sorcerers.