My Mrs makes vinegar from fermenting second run-offs or squeezing the bag of fruit after fermentation, wine or cider... and its bloody amazing. It's actually really simple... The main thing is to aim for an ABV of about 9% for your starting liquid we use clean vodka to top it up if needed. Fill a kilner jar 3/4 of the way with what you want to make vinegar from. Buy a bottle of Braggs and Aspall RAW cider vinegars, shake them up and throw in maybe 100ml of each in, to drop the pH a touch and add the culture present in the bottles. We also add in some of our house brett culture. Then just cover the jar with cheesecloth, secure with string or an elastic band, and leave it. It takes about 8-12 weeks to complete. You sill see a scoby (culture disk) form on the top of the liquid over time - that's a good sign, and you can cut that up with scissors and throw it into future vinegars to help speed up the process. I'm sure she would explain it better, but that's the gist of it! I'll do my best to answer any other questions, or ask her haha
Also it's a good idea to have a calibrated pH meter around, so you know when it's done as bottling too early and activity continuing without supplied oxygen spoils the product. Also pH meters are good anyway.