To connect to Orchestrator with client credentials or machine key, click More Options > Connect to Orchestrator. To activate a local license key, click More Options > Standalone Options. A new page opens in your web browser.
Complete the sign in procedure, and, when prompted by your web browser, click Open UiPath to return to Studio
Check out the document (Signing in to Your Account)
In Orchestrator, navigate to the License page at tenant level or host level.
The License page is displayed. Click Activate Online.
The Activate Online window is displayed.
The Installation ID field is automatically populated with the unique identifier of your Orchestrator instance and is not editable. After receiving a license key from UiPath, you can proceed to activate your Orchestrator instance
As suggested you can download the enterprise studio as well…whoch will be available in product ownloads in orchestrator…you will find product downlods option on top right of the orchestrator .where you have ahelp icon…click on it
And now coming to why to connect to orchestrator…is to use assets …or to run the process from assistant…else if you have only studio then only you can run the bots…