If your teacher has allowed it you can create a zip-file, that contains all the files you want to submit.

To create a zip-file, first create a folder. The name of the folder will become the name of the zip-file. Put the files you want to submit in to the folder you created. There should be no other files in the folder (other than the files you want to submit). 

If you're on a PC using Windows, right-click the folder and in the menu that appears you should select Send to and then under that menu select Compressed (zipped) folder.
You then should see a zip-file with the same name as the folder you created appear. You should upload this zip-file on the submission page. If your teacher has allowed handing in zip-files, the file will upload.

If you're on a Mac or Macbook, right-click the folder (or hold down Ctrl while clicking the folder). In the menu that appears choose Compress "folder name". You then should see a zip-file with the same name as the folder you created appear. You should select this zip-file to upload on the submission page. If your teacher has allowed submitting zip-files, the file will upload.