Strength: Strength is the modifier that determines just how much damage you can inflict on a monster. With 1 Strength you will always slightly wound a monster. With 2 strength you will either inflict 1 damage or 2 damage granted that you hit the monster. While other stats may seem important if you are going to be hitting monsters dont neglect strength the quicker you take down a monster the less problems likely to occur.
Endurance: Endurance is the modifier that controls your max health. Each point of damage will take off one point of health from your endurance. Always a good idea to at least have enough points in this to survive a hit or two from monsters that you are fighting.
Portage: Portage is the modifier that determines how much you can carry. Depending on the item's size it may take up different amounts of portage. The least important stat just make sure you have a few points more than the port you are using. If you get sapped for portage you could end up carrying nothing if you have too little portage.
Speed: One of the most important stats in GC. This stat determines the likelyhood of landing a blow and in addition to that just how far you can approach a monster and visa versa. Early on 20-25 speed can go a long ways. As long as you have a weapon with a long reach and keep your distance you will find most monsters wont be able to approach you close enough to hit. I will attempt to explain keeping track of your distance from monsters in a later tactics post. Speed also determines whether or not you will get uglied by ugly monsters.
Magic: Another important stat to GC. This determines the spells you will receive from the witch and how much she favors you. Below 4 magic you will get nothing from her. The lower spells such as invisibility and flight have magic requirements of 11 magic and unless you have a fairy these are the spells you will be gunning for early on. 15-20 magic will take care of most of your real early spell needs. Magic also determines how much quake affects you, how deep you can teleport into the cave, and can affect monsters reacting to you while invisible.
Additional Stat Info: Your total number of stats determines how many improvements you will get from monsters you kill. Improvements count as stats. Total stats also determines how siren song will affect you.
Finding the right Stat proportions: A good tool in figuring out just how much of each stat you need is the Thane List. Watch what others do and try to mimic and improve upon what you see on this list. Pay attention to how fights go for you. If you are taking damage and could die, improve endurance. If it takes you 50 clicks to kill something because you arent doing a lot of damage improve strength. Spells are always a nice thing to have so keeping magic high is always a plus. Watching speed so monsters can't get in your face is probably the most important thing you can do.