Ok i really suck at mario kart, i havent played since mario kart 64 and thats a long time.. please check out my video and give me some pointers on what i need to do better.. and what is the best kart/character to use  https://youtu.be/ZPQDzXojS8k

Try taking advantage of drifting. You seem to struggle because of the awkward turns you take while driving

You'll eventually pick things up. Have fun!

Yeah drifting really is crucial... it's actually fairly easy to get a handle on it after 30 minutes or so. If you go to the "info" option on main menu you can read how to drift and a couple other things.

1.) Always drift around corners. You should never try to turn more than like 30 degrees without drifting. Turning without drifting should be for making small adjustments only.
2.) Hug corners tightly. Racing is all about taking the shortest path. Take the insides of every turn.
3.) Those boost panels in Mario Kart Stadium are a beginner's trap. Sure, you get a temporary increase in speed, but you end up taking a much worse racing line because they're on the outside of the corner.
4.) When you have boosting items like stars or mushrooms, use them to go off-road and cut corners, if you can.
5.) The boost at the beginning is triggered by starting to hold A in the middle of the countdown, during 2. Like, right in the middle of 2's appearance.

As for characters, there's not really any "best combo", since there are always trade-offs in your stats. If you're getting hit a lot, prioritize acceleration, if you're not good at turning/drifting preemptively, take handling, etc.

Thanks everyone so drifting is the key?

Yes! Drifting means you can make tight turns without losing much speed and as a matter of fact, in MK drifting means a small speed bonus if done correctly.

Observe Zebra Gamer's drifting:

Drifting is key, also pressing the minus button during the cart selections shows the cart's stats. Use the stats to your advantage. Also focus on acceleration and traction

Drifting is pretty much half of the reason why I am good at Mario Kart to begin with so practice it on the lower difficulties so that way it feels natural to you.

Your turns are awkward. Drift more from left to right until you get it down to a science. Shouldn't be too hard. Also, try to hit the boxes as much as possible because the distance between you and your opponent mostly comes from what you hit them with. Also, try to get as many boosts as possible that the level can provide.

Get to know the maps more. If you go in not knowing anything you might get caught off guard. Lastly, be more aggressive.