Your mains stopcock is very important it controls the main flow of water into your home. If you ever have a plumbing emergency like a burst pipe the mains water supply needs to be shut off with the stopcock as quickly as possible to minimise damage.
You should ensure your home has at least one stopcock; most homes have a stopcock inside the home and outside the home. Most newer homes will have an external stopcock outside. Some older properties will share an external stopcock, so if you shut it off, you could be shutting your neighbours off as well. External stopcocks should only be turned on and off with the correct tools.
Internal Stopcocks are usually located underneath the kitchen sink you should make sure you know where the stopcock is and that it turns and closes. Stopcocks get very little attention and can seize up which means the mains water can’t be shut off which is essential in an emergency. If your Stopcock is not under your kitchen sink, then it’s likely located elsewhere on your property make sure you know where it is.