We are leveling up mid-adventure.
At 2nd level, everyone gets the average of their hit dice, rounded up. So d4 means 3 hit points, d6 means 4 hit points, d8 means 5 hit points, d10 means 6 hit points and d12 means 7. Add (or subtract) your Constitution bonus from this score.
You get skill points for leveling up based on your class, plus another skill point for being human, plus skill points equal to your Intelligence bonus.
Other improvements, like spells per day, additional bonus to attack, new feats, and so on, are based on your class.
Google "D20" to find a number of sites with complete information online.