First, welcome to the game! It's not complicated, but it is complex - that is, no one part is hard, but there are many,
many parts. But have faith - you'll make sense of it as you start to absorb one part after another, it
will all make sense.
Right.
So, as mentioned above, every Class has a fixed number of Skill points that they get each level: Fighters get 2/ (among the lowest), Rogues get 8/ (the highest), etc. etc.
To this, you add (or subtract!) your Intelligence
modifier (the "+#" part, not the actual value!).
And if you're Human, you add +1 more - Humans be like that.
Lastly, at Level 1 (only), you take 4x this value, just to get you started.
Skills also have a max value, depending if they are "class skills" (as listed under your Class), or "cross-class skills" - a skill not listed under your class. Max value for Class skills is 3+Level - so at Level 1, you can take 4 ranks max, at Level 2, 5 ranks max, etc. Max value for cross-class is half that, and spending 1 point in a cross-class skill* only gets you 1/2 a rank.
(* For multi-class characters, this is determined by the class they are currently taking. So a Fighter/Rogue can spend 1 pt per 1 rank on Open Lock when they are leveling up Rogue, but must spend 1 pt per 1/2 rank when leveling up Fighter.)
(Example: A fighter has Jump as a class skill. At level 1, they spend 4 SP and get a 4 in Jump, the max. They also want to take "maximum" Balance (to fight on uneven surfaces!), but that's a cross-class skill, so they spend 4 SP on 2 ranks of Balance, the max for a cross-class skill.
Next level, they spend another 1 pt on 1 rank of Jump (for 5 total), and could spend 1 pt on Balance, for 2 1/2 ranks total - but if the player is smart, they'll spend that 1 SP on something they can use now (1/2 rank does nothing), and spend 2 SP next Level on +1 Balance (2 half-ranks at once), giving them a total of 3 ranks in Balance, the max for a cross-class skill for Level 3.)
So...
Sorcies get a base 2 SP/level. Intelligence 10 has a +0 modifier, so that math is easy - {(2+0)x4} = 8.
(If your character is Human, you add +1 for (2+1) = a base 3 Skill Points/Level, and 12 at Level 1.)
At Level 1 (only), that's multiplied x4, for 8 (or, if Human, 12) to start. Woohoo! \o/
Every level after that, you get that base number each Level. Gear doesn't modify that, but if your "+1 to a stat every 4 levels" (or any other permanent change to your Base Intelligence Modifier) changes your Int Modifier, that changes all
future Skill Points - you don't go back in time and learn more.
And we remember, max ranks is 3+Level (and that /2 for cross-class skills*).
(* Multi-class characters have some additional rules about max ranks for cross-class skills; essentially, if the skill is a class-skill for any of their classes, it has no cap, but the cost is still 1 SP for 1/2 rank for cross-class skills for that level, etc.)
So, for Level 5, you get 8 (at Level 1) +2 +2 +2 +2, or 16 Skill Points (or 24 if Human) with a max rank of 8 (or max of 4 for cross-class skills).
Wow, do you really forget the first time you read the PHB?