Why don't my brakes work?
No matter how hard I pull on the brakes, I can't stop
There are a few reasons your brakes may not be making contact with your tire.
First, double check that your brake cables are connected, this happens more often then you would think.
If you have traditional brakes your cables may just need to be adjusted (tightened if your brakes aren't touching the rim when you squeeze the handle), or, you might need new pads if they are worn out.
If you have hydraulic disk brakes you most likely need to add additional brake fluid.
You should always give your brakes a little test first thing when you jump on your bike!
Its a metaphor for life.
Or just get new brake pads and/or make sure the cables aren't trashed
you need to tighten them. It's a pretty universal process. It can be fairly fiddly, having another person help you tighten it whilst you hold the pads just above the wire. another guess at this is that you may need new brake pads, they are consumable and can wear down. tightening them works until you need to buy new ones, it's basically re-calibrating them. The closer to the wheel they are, the more likely they are to stop it, so I recommend you look up a guide on google "How to tighten bicycle brakes" or how to calibrate them. I'm not a mechanic, but I have experienced this issue with my bicycle!