Hi, everyone, 

I'm fairly new to dnd and I was confused about how natural weapons and unarmed strikes work and I need to know for a build. Do Natural weapon attacks count as Unarmed Strikes?

In general, no. Unarmed strikes don't involve weapons.

In practice, for player characters the answer is almost always yes. Racial traits, spells, class features and magic items that grant natural weapons usually make an exception to the unarmed strike rules that allow you to use the natural weapon.

Thanks in case your wondering it's an Ascendant Dragon monk ( UA), Beast barbarian multiclass specifically I wanted to know if this ability of the monk's Draconic disciple feature, "When you damage a target with an unarmed strike, you can change the damage type to acid, cold, fire, lightning, or poison." works with the natural weapons of the Beast Barbarian

In this case the answer is no. The Beast Barbarian's ability specifically calls out the natural weapons as a simple melee weapon:

When you enter your rage, you can transform, revealing the bestial power within you. Until the rage ends, you manifest a natural weapon. It counts as a simple melee weapon for you, and you add your Strength modifier to the attack and damage rolls when you attack with it, as normal.

This completely excludes it from working with any feature that requires an unarmed attack.

Contrast Emmber's post about the Beast Barbarian with the description for the Tabaxi's claws: "In addition, your claws are natural weapons, which you can use to make unarmed strikes."

Similar wording exists for the natural weapons of the Leonin and Minotaur, the claws from the Dragon Hide feat, and very similar wording for the natural weapon option in the Alter Self spell.

So barring any official ruling otherwise, I would say that if the description of a natural weapon will tell you if you can make unarmed strikes with it or not.

If it says you can make unarmed strikes with it, it counts as an unarmed strike. So it would be affected by Martial Arts and other unarmed strike effects. If not, it usually specifies on what the natural weapon is.

But wait... The Form of the Beast feature says the natural weapon is a simple melee weapon, so wouldn't it be affected by Martial Arts? Monk weapons include simple melee weapons without the heavy or two-handed properties, which the natural weapons are not. Therefore, the Beast's natural weapons (and anything that works the same way) are monk weapons.

The Beast Barbarian's natural weapons would work with Martial Arts - yes - but Draconic Disciple doesn't because it specifically calls out unarmed - and that's what the OP was asking about.

Natural weapon attacks do not count as Unarmed Strikes unless noted otherwise.  There is an official ruling in the Sage Advice Compendium;

Are natural weapons considered weapons? Things designated as weapons by the rules, including natural weapons, are indeed weapons. In contrast, unarmed strikes are not weapons. They are something you do with an unarmed part of your body.

A Dev also confirmed it on twitter;

@JeremyECrawford A natural weapon (a claw, horn, bite, etc.) is not an unarmed strike.

@JeremyECrawford Rules on unarmed strikes have no bearing on natural weapons. Some exceptional things in the game count as both unarmed strikes and natural weapons. For example, a tabaxi's claws are natural weapons that can make unarmed strikes.