You may not find your pelvic floor muscles immediately. Many people have to take their time with this. Remember, you are searching for muscles you may not have been aware of before. Your muscle may be weak, so for now your goal is only to locate your pelvic floor muscles. When trying to find a new muscle, especially a weak one, most people tighten other muscles too.
Some people clench the fists or teeth, hold their breath or make a face.
None of this helps. It is very tempting to use other muscles, especially stronger ones, to support small, weaker muscles such as the pelvic floor muscles. However, using other muscles interferes with learning how to use the right ones. It is best just to relax your body as much as possible and concentrate on your pelvic muscles. Most people who are learning to control their pelvic floor muscles tense their belly muscles at the same time.