Hello. I use to play with this Udyr build. First of all I like to start with life steal so I can restore my HP when I'm at first levels. Next is the razor... I use them to get money faster from minions, that's very importan because if you can't get easy kills you can build a good gold from them.
After that I use to get my boots with speed, that's very important for the turtle to restore your mana and hp.

Well I like to start with a good speed and smash arround with the bear. As much speed you have for the bear stance better, because your hits smash only for 1 sec every 6sec per champ ... So if you have good speed you can hit them for 2 times and don't recive any hit.

Well I use to take Ignite because when someone have low hp use to run, burn him and you will take the kill.
Exhaust, because our Udyr scare a lot :D . You can slow them and make a greater damage using tiger stance and bear, they will be owned by you if you do it well.

Well as I said I like to start with life steal, and the faster way to get money (if you can't take kills) are the minions, and the pasive of the latern is great for that.
Boots, they give us speed, this speed can be used with turtle to restore our hp and mana.
Okey my next item, the hummer, is great for udyr as off tank. Why? Because Udyr is very good to take down turrets! But as I told you before, people use to run from Udyr (best champion,in my opinion, 1v1) that will slow their speed and you will be able to take them down easy and faster, they will not be able to run from you :D.
Next one are for damage, as more damage we do faster we will take down the turrets and our enemys.
At final stage we pick up more speed and critical damage. If we have all the items we can sell the latern and pick some more damage.

Bear, you can make good asists, run, stun, stop ultymates etc... Is great for start if you have a good partner at your line. !Important if you think to jungle you will have to change this for turtle and no vampiric scepter for start you pick armor and pots.���¡!
Next Tiger, because I like to use tiger and no phoenix, but also is great in 1v1 battles.
Turtle, you use it to restore hp and mana when you fight under turret with minions.

Well you can help to your team with Udyr, or your team can help you. For example you can gank from hiden place with the bear stance, which incrase your movement speed's and stun the enemy, so your team can run or atack...
If in your team you have ashe, she can stun with his ultymate and help you to get closer to the enemy.
The best is the way to stop ultymates or draw (from Fid). I use to stop Katarina's ultymate, or when Fid is drawing a champ from my team I stun him so my buddy can run.
The best of all is the easy way wich Udyr take down the turrets, so use to flip the line and take down as much turrets as you can.

Udyr incrase his speed when flip's his skills, so try to use bear stance whe you are close to the enemy, and then flip tiger, then again bear and tiger. This will give you bonus speed wich will take down very fast the enemy.

Good luck, excuse me for my bad english :)