The Files application   is preinstalled by default on your device and lets you see the content stored on your internal memory but also on your external USB devices (USB stick or hard drive connected to the host port) and on your network.  

To transfer a file / folder or agroup of files / folders: 

1. Launch the application and browse to where you can find the content you want to transfer. 
2. Tick the box(es) beside each file / folder that you want to transfer. 
3. Select copy (content will be duplicated) or cut (content will be moved) 
4. Select the internal memory of your device and then the folder where you want to paste your content. By default the location is the source of the internal memory. 
5. Finely, press paste to paste the content. A in process window will be displayed, wait until it's complete or press Cancel to stop the operation.  

Please not there are other applications available on the  Google Play™ that you can download to do the same type of operation.