I believe that there was an issue while downloading the Google Cloud SDK, in that case, I will be explaining starting from the installation process.
1.First, download the official Google Cloud SDK archive file from here(https://cloud.google.com/sdk/docs/quickstart-macos).
2. Unzip the archive and save it at your desired folder.
3. Now open the folder which contains your unzipped google-cloud-sdkfolder in the terminal.
4. Run the command ./google-cloud-sdk/install.sh and give yes to all further prompts and you are done.
Now, just type gcloud -v to verify your installation. If you find your gcloud version in your terminal, then you have successfully installed google cloud SDK.
Now the command gcloud will be available globally anywhere in your terminal!