Welcome to the guest questions forum.
Using a file explorer app, such as ES File Explorer, you will have to navigate to where the screenshots are, usually Storage/sdcard0/Screenshots or Storage/sdcard0/DCIM/Screenshots. Then just select the files you want to copy, select copy, and navigate to Storage/sdcard1/Pictures and select paste. (The folder could also be Storage/extsdcard/Pictures, but you get the general idea.)
Hope that helps!