IP, or Improvement Points, are the building blocks of raw levels. Both stats and skills have raw levels, which essentially determine how good you are at that skill, and how much you reflect that attribute. Any number with a following decimal is a raw level. From practicing an action, you have a chance to gain 1 IP. Gaining 1 IP increases your raw by .01. So, every 100 IP is 1 raw level.
To practice a skill, simply use it. For example, to practice blades, find a knife and start attacking some poor dog. If the dog presents enough of a threat to give you a solid challenge, but is not so overly threatening you have no chance of even scraping it, you will most likely gain 1 IP in blades after taking a few swings with your knife at the dog. To practice something like repair, find a busted up weapon, and trying fixing it back to its origional state. If the weapon is less complex to fix than a space station, and is more complex to fix than a crooked picture frame, chances are good you will gain 1 IP in repair from fixing that weapon.
To practice a stat, you will need to use one of two methods. Scattered throughout the world in many different shapes and forms, you can find 'gym' machines. These are objects are strictly designed to put one of your stats to the test in order to improve it. You can find them in the shape of a weight set, a supercomputer, or an arcade game. Using these items gives you a chance to gain 1 IP in that stat, however, upon creating a new character you are only given a possible 805 IP that you can gain for 'gym' machines. Meaning if you were to play mastermind with a supercomputer 805 times in a row and gain 1 brains IP each time, you wouldn't get a brains IP on your 806th time winning, nor any after it. The alternative method to gaining stat IP, is to use a skill which relies on the stat you wish to train. So, very rarely while attempting to stab something to death with your spear you will gain a reflexes or endurance IP instead of a spears IP.