I will describe here a couple of ways to upload files to VM.
1. Upload file using browser window 'Upload file' menu
I normally use 'Browser Window' to access command line on Linux VM. It has menu option 'Upload file', which will upload selected file to your user home directory. Unfortunately, it is very slow way of getting file to VM.
2. Upload file using 'Storage Buckets'
Storage Buckets are the basic containers that hold your data. Everything that you store in Cloud Storage must be contained in a bucket. You can use buckets to organize your data and control access to your data. To upload file to Storage Bucket we will use gsutil tool.
gsutil cp [filename] gs://[DESTINATION_BUCKET_NAME]/
To download file from Storage Bucket run
gsutil cp gs://[BUCKET_NAME]/[filename] [SAVE_TO_LOCATION_PATH]