and also im having trouble punishing people who use short hop aerial attacks(such as nesse's nair)i try to use a nair put some attacks have priority over captains nair. do you have any advice
If I were you, I wouldn't try to beat out a short-hopped nair. Instead, I would be a bit more defensive and shield their nair and then follow up with a punish. We can go for a forward tilt, one of our own aerials, or a grab (maybe a dash grab depending on the space).
Don't be overaggressive against Ness because he can easily punish you for it.
what approaches should i use instead of a dash grab
As for approaches outside of dash grabs, I like to use dash attacks, running and shielding, neutral and back aerials, and surprise Falcon Kicks.
The dash attack allows Captain Falcon to set up a combo and follow up with a smash attack or aerial.
Running and shielding is pretty useful for predicting opponents and going against projectile heavy players; I used this against a Fireball spamming Mario and he couldn't do much when Falcon was in his zone.
Neutral and back aerials allow for Falcon to space and these are pretty effective attacks in helping Falcon get closer to his opponent. I am more of a fan of the neutral air due to the better spacing and the fact that it hits twice.
Falcon Kicks shouldn't be spammed as they become heavily predictable, but they are good surprise attacks to use and it enables Falcon to follow-up.
One thing I recommend; don't
always use dash grabs and mix up your approaches. While the dash grab is incredibly effective, opponents will follow on, bait you, and then punish you.
EDIT: I made a mistake. Definitely use dash grabs as it is an effective tool for approaches, but don't always use it because it can lead into a very hard punish. However, I think there are several match-ups where dash grabs are neutered.