[Imported photos very distorted]

I just purchased the Affinity program & I'm considering design creations for a company located in Australia. Being very new & unfamiliar with the capabilities of the art & design programs, my question is certainly very elementary. I apologize if I misuse or don’t understand certain terms, but I do appreciate the opportunity to ask questions. The discussions & answers I've read, even if out of my realm, are very kind, which go a long way towards the comfort level. I want to make seamless textures & designs for this company; however, some of the tutorials available are descent but many times, the creators present the information very quickly & assume that one already knows the ends & outs of the program they're using. I am a secondary math teacher & learning abilities cannot be an assumption, especially when the person presenting is quite knowledgeable of & has experience with the subject topic. The tutorials I've viewed in the Affinity program are very thorough & cover the topics well...I commend the video creators for their ability to convey the information. I understand the Affinity tutorial for making seamless textures & I've watched the video several times. My problem is that when I import a photo, it's very distorted... I'm sure the solution is a simple one, but I can't figure how to make my photos clear as is presented in the video. I know there are many topics on features & tools & thank you for making those available, but I must be overlooking the topic on how to reduce the distortion. I would greatly appreciate direction on finding this information...thank you for your time & attention to this matter.