@Namechanger1002 I came back to look at this thread on the off chance and saw I’d missed your original message. So sorry! Hope this is still helpful anyway.
So wild camping essentially means camping somewhere that isn’t a designated campsite. In England, the only place this is actually legal is Dartmoor.
However, unofficially, as long as you leave no trace (I mean, really leave no trace: remembering to search the ground to make sure you haven’t left any tiny bits of ‘micro trash’, like the small corners of a hot chocolate packet, or a couple of oats from a porridge sachet, and of course absolutely NO toilet paper etc. - there is a wealth of leave no trace camping resources online) a blind eye is generally turned on backpackers wild camping on National Trails.
My tips would be to ask other hikers if they’ve passed any good spots, keep an eye out for flat, secluded patches slightly off the trail, and pitch your tent fairly late in the day and make sure you pack up early. There’s also a lovely South West Cost Path Facebook group where people share wild camping spot suggestions. Looking at your google maps on satellite/terrain mode gives you a good idea of the area, too.
I met a woman hiking the SWCP solo who was an amazingly brazen wild camper. She would pitch her tent at 6pm, make herself dinner, and sit there chatting to the evening dog walkers who passed. Very inspiring! I preferred to choose a spot, make myself a hot chocolate, and then sit there looking at the sea/ reading until it was getting dark before pitching my tent. Everyone approaches it in different ways. I only did it a handful of times, but it was a lot of fun.
I hope you manage to do it! You can definitely do a lot, and have an amazing experience in 10 days. Good luck!