If you are concerned you may have cancer, the best thing to do is to go to your GP and talk to them about your symptoms and if you need any tests, they will refer you for them.
If it is bowel cancer you are worried about, I think you can get a home FIT test, but all that will tell you is if you have blood in your stool, which could have many different causes even if you get a positive result, so if you do get a positive result, you will just have to go to your GP so they can determine if you need further investigations for any condition, cancer or others, afterwards. If it's negative, cancer is highly unlikely.
But it's probably best to go straight to your GP, who may find a different cause for your symptoms, if you have them, without even doing the FIT test.
If you are just at the age at which bowel screening is indicated, there is apparently a helpline you can ring, but I'm in Ireland, so I don't know much about that.
