I am so: Transport endpoint is not connected. Please help me. Thanks

In general, object storage solutions like Spaces are not meant to be accessed like a file system. They are API driven and most often used programmatically. Block storage, on the other hand, works almost like attaching a USB drive to your laptop. It gives you new drive with expanded storage. Check out this tutorial to learn more about the differences between the two and if object storage is right for your use case.

If your use case really requires mounting your Space like a local filesystem, s3fs-fuse is probably the tool you are looking for. On Ubuntu, you can install it with:

sudo apt install s3fs

You’ll also need to get your Spaces access key and secret key (see here).
Then add those credentials to ~/.passwd-s3fs, create the local directory, and mount your Space:

echo $SPACES_KEY:$SPACES_SECRET > ~/.passwd-s3fs
mkdir -p /path/to/local/directory
s3fs your-space /path/to/local/directory -ourl=https://nyc3.digitaloceanspaces.com -ouse_cache=/tmp