You can set the post or page URL by editing the "Slug" option inside Document Details.
Navigate to the document you'd like to edit, and look right next to the Title option:
Best practices usually include:
Relatively simple and short (think ~60 characters or less)
Something memorable that people might later type in to visit or recall directly
Include keywords or post titles where appropriate (but realize it's not a huge ranking factor)
Read this Moz guide for more details.
Also, please note this is currently only available on WordPress and HubSpot connections.