I’m a little lost trying to create specialty arrows in the Homebrew section. I’d like to set up fire arrows, silvered arrows, explosive, etc. There are tabs for making weapons but not ammunition. 
Little help?

PHB page 148.

You can silver a weapon or 100 pieces of ammo for 100 gp. This covers materials and expertise.

As for the others you will have to make it up as you go along. 

But flaming arrows are easy. Just wrap a rag around the tip and cover in pitch(bitumen) or oil. Make and light as needed.

For explosive that is a bit beyond field expediency. You will more than likely be looking into magic.

Quote from TheGnome5786 >>

PHB page 148.

 

You can silver a weapon or 100 pieces of ammo for 100 gp. This covers materials and expertise.

 

As for the others you will have to make it up as you go along. 

But flaming arrows are easy. Just wrap a rag around the tip and cover in pitch(bitumen) or oil. Make and light as needed.

 

For explosive that is a bit beyond field expediency. You will more than likely be looking into magic.

 This isn't helpful as OP is talking about doing things in DnD Beyond.

@OP Have you tried making a weapon that you name "Arrow of XXX" and then just give it the properties you want?

Since Ammo is not included yet in the creation program just use the weapon entry and describe it as an arrow.

What might work better is equipping multiple quivers to your character sheet, renaming each quiver things like "Silvered Arrows", "Exploding Arrows", "Erotic Dance Arrows", and the like.  Then create custom actions on your sheet for each arrow type, and/or a feat that describes each special arrow you can create.  You'll know what your arrows can do, and you can store normal arrows in each named quiver to keep track of how many of them you have.