Abilities in general

[the_prophecy]

Can i use Abilities, marked on a warscroll only once per turn? And can i use more than one ability on a warscroll or is it just one Ability. Because the Cauldron of Blood has several different Abilities. Can i use every one or only one and/or the same one several times?

[Oppenheimer]

It depends on the wording of the ability. If it doesn't say once per turn or in the combat phase or something like that then you should be able to use it as many times as you wish. 

Edit: Command abilities are a bit different.

[amysrevenge]

Abilities tell you when and how to use them.  The closest they get to ambiguity is that sometimes things that you can only do once are only implied to be once rather than explicitly once. 

For example, the Strength of Khaine ability says: "In your hero phase the Cauldron of Blood's Death Hag can pray to Khaine." Then it goes on to describe the effect.  This is the only bit where it talks about when/how.  There is no explicit statement that you can do it more than once, so you do it once.  (There is also no hint that the use of this ability is affected or limited by other uses of the Blood Shield, Witchbrew, or Pact of Blood abilities.)