Until the brew gets going the culture needs to be protected from contamination which the mother brew provides. If you don't have any mother liquid then vinegar may be added.
If you don't have enough mother liquid you can use distilled or non-fermented vinegar (15 ml / 1 tablespoon per litre of brew). If you are not sure what your bottle of vinegar is then boil it for 10 minutes and allow to cool before using. This will kill any of the live components.
Using vinegar is only used to keep the culture alive if you don't have access to another culture. The flavour of this brew may not be so good but it may at least keep your fungus alive for you to make further brews with.
If you are concerned about flavour use white distilled, white wine or cider vinegar, strong malt vinegars are not so good.