After you've downloaded the installer for UiPath, go ahead and double-click on it to get the installation started.
At the first installation screen, select the "Custom..." installation instead of "Quick...". Then click Configure.
Select the "Automation Developer" option, then click Install.
After the installation has completed, click Launch UiPath Studio.
Once UiPath Studio launches, you'll see a screen called "Connect to Orchestrator". Click "More options" in the bottom left corner of the window.
Click the "Standalone Options" button.
Now, go back to the email that was sent to you after you requested a UiPath license. (Follow these instructions if you haven't requested a license, yet)
In that email, find your license code, then enter the code under "Add License Key". Leave "Automatic (recommended)" selected, then click Continue in the bottom right corner of the window.
Then, you should be all set to go!