In Meridian 59 leveling is two separate tasks: Hitpoints and Spells / Skills.
The experience you earn while killing monsters is put towards your hitpoint level.
Your total hitpoints are based on your stamina stat. You are able to gain a maximum of 100 + stamina hitpoints. So a player with 40 stamina will have a maximum hitpoint level of 140.
While killing monsters that give experience, you will also gain training points. These training points can be spent to improve your spells and skills.
Spells and Skills
Your spells and skills level when you use them. Your spells and skills can also be improved by using training points. You may gain training points by killing monsters or logging on every day.
Some spells (touch spells and personal enchantments) will level on their own if you use them while killing monsters.
You are also limited to a certain number of skill levels depending on your intellect. Roughly you are able to learn 10 + (int / 5) levels worth of skills.
Here is a chart for reference:
Even if you have all of your levels you are still able to purchase spells from level 1 of any school. However, level 1 does count towards your total levels so do not buy any level 1 spells until you already have all the other spell levels you want.
It is important to remember that only the three best percentages in your current level count towards the total. So if you are trying to attain the next level of a school you should focus on just 3 spells in your current level.
You can also check you current progress with your school’s priestess.