I need some advices to build my first sword it would be a viking sword. Any help would be appreciated.

Wow, where to even begin. Do you have any knowledge of metal work? Knife making? Heat treating? Forge work? How to run a grinder? What tools do you have access to? All of these things make a difference in how you could/would/should proceed. I do not think that you are going to be able to get the information you need via a discussion forum like this unless someone who actually makes swords were to sit down and do a series of detailed posts (articles really) on how to make a sword. Even then... I will, however, point out the old pioneer standby that being Dr. Hrisoulas's The Complete Bladesmith book. Some of the information is inaccurate and some out of date but to my knowledge it is still the only book of its kind out there and viewed by most as a pretty good jumping off point. Hope this helps.

i just know how to run a grinder but the rest is new for me...

and a detail that i should say ... i'm 16 years old.

What difference does your age make?

If you are willing to learn, willing to work, and not afraid to screw up along the way...then it makes no difference if your 16 or 60. Just grab the bull by the horns and go to it.

I suggest you set your sights a little lower to start with. Start by grinding out a knife. Pick a design you like, get a leaf spring (from a car), a piece of tool steel, or some other relatively high carbon steel and draw out what you want your knife to look like. Then wander over to your grinder and start trying to make the metal look like your drawing.

Sound easy? It isn't...but that's life and if you keep at it, you'll be fine.

Once you get that done, play around on your grinder with other metals, bigger pieces, etc. You can make a lot of nice stuff without ever touching a forge and anvil. The Complete Bladesmith is a great book, by the way.

For blacksmithing (which you'll need to understand for the forge work stuff), there are a ton of good books out there and a class or 2 would be a good investment if you're serious about getting into it.