Just got Skyrim yesterday and I came upon those 3 stones to select my skills. In Oblivion I was able to select my 7 skills early on. If I want different skills, did I miss my opportunity? Thanks.

There's 13 of those stones in the world. Only 1 can be active at once, and you can change them whenever you want by activating them.

skills improve by using them. you can only get perks for specific things by leveling up (look in your skill tab)

Just start using the skills you'd like to level in. The three stones only make the associated skills level up faster than usual.

you don't really select em like in oblivion, you can activate these stones that give you some benefits depending on how you want to play, you also get to pick a perk every level for each skill, and how to do that molds your character, racial traits also define your character a bit and you can determine how much magic, stamina and health your character has as you level up, so thats how it works...you don't pick skills, you just more or less put perks into the skill trees you like and use thoe skills you like and thats the main way you level up those skills, however there are skill trainers you can use as well like fendal in riverwood is an archery trainer..so thats another way to help you level up that skiil.

skill stones are like the star that you were born under in Oblivion. each offers different bonuses.

when you first leave helgen you come across 3 stones. thief, warrior and mage.

pick the one that has the skills that you wish to progress faster.

as you discover more stones through your travels you can change skill stones as your needs change.

i prefer the lovers stone that lets all skills progress 15% faster.

stats and major/minor skills are no more, now it's perk points and the usual leveling whatever skills you want.