can you put a photo in a different photo

For simple objects you can do it in Preview, that comes preinstalled on your Mac.

• Open the photo you want to suppose in another photo in Preview and use the selection tool to select the part you want to put into another photo, the copy to to the clipboard.
• Now open the destination photo in Preview and paste the copied section into the other photo, drag it to the position you want and drag the size corners to adjust the size.

For photo realistic results it will not suffice and you will need an editor with advanced tools for graphics composition.

Yes, but not with Photos. There are a lot of photo editors that will do this for you ranging from the inexpensive to the industry standard.

Search Photo Editor in the App Store