Kardell is a good hero to learn how to play with.
Start by selecting the distance upgrade first.
It will help you in terms of defence, and especially try fight in the same lane as melee opposition, taking pot shots at them and keeping their hp low for assasinate.
Scattershot should be used for farming and pushing, its a great option to use when there are alot of creeps and u all of a sudden kill the enemy creeps with one scattershot and then ur creeps are free to attack heroes.
A build that i have seen on the dota forums for kardell start like this :
1. gauntlets of ogre strength
2. circlet of nobility
3. flask of sapphire water
4. clarity potion
those u buy once u select kardell
after awhile/wen u can afford it
1. point booster
2. bracer
3. staff of wizardry
4. boots of speed
5. void stone
6. robe of the magi ---> euls scepter of divinity
now u have alot of mana so use scattershot to farm
then u buy
1. ultimate orb
2. ultimate orb
3. eye of skadi
4. quarterstaff
5. sobi mask
6. robe of the magi --> oblivion staff
7. guinsoos scyth of vyse.
So now u have a hero with decent hp, attack and frost attack aswell as the ability to turn ur enemy into sheep with the scyth of vyse. and obviously its ulti -> assasinate.
Its very important in the beggining not to die, and its reasonably easy with kardell because if you upgrade his range then he can stand far enough back and pick off damage from the enemy.
Best tip i can give is to not die, and watch the mini map for when the enemy has dissapeared from other areas of the map, which means they prob on their way to gang u. and never buy a recipe before an item.
Cant think of 2many other things, but feel free to ask.
Laterz
J