Can someone explain how to use a black salamander? Do you only need one black salamander and then lots of tar to use? Each attack does it use one tar?

Any attack style uses the same type of tar.

You only need one salamander. You'll equip it (2h) and it shoots tar, so you'll need one tar for each attack.

And ofcourse, the tar gets lost in the process. By selecting different attack style (just like with any other weapon), you can decide wether it be magic , ranged or melee you hit with.

and just incase you didn't know, Tar goes in your Ammo equip slot.