Help! I want to put someone in a different picture.

Open both images, mask or extract person then move it into another image. Not straight forward to explain here to newbie. Try to find tutorial how to move person from one image to another.

Use menu File>Place to pace the persion's image into the image document you want them in. Mask the person in the placed in image to extract them. Then transform the person places in smart object layer to scale and position them into the document's composite image.. 

Have a look here:

https://www.google.com/search?ei=Q_q6X9HtB7WwwbkP5p6E-As&q=photoshop+take+a+person+out+of+one+picture%2C+and+put+them+in+another&oq=photoshop+take+a+person+out+of+one+picture%2C+and+put+them+in+another&gs_lcp=CgZwc3ktYWIQA1DQ0gJY0NICYLHUAmgAcAB4AIABAIgBAJIBAJgBAKABAaoBB2d3cy13aXrAAQE&sclient=psy-ab&ved=0ahUKEwiRm8vprJftAhU1WDABHWYPAb8Q4dUDCA0&uact=5

the actual pics would really help a lot mate