When you have invited Agents to your account Route will start to automatically distribute leads among those agents.
You can also manually change and assigned a lead to an agent when importing a contact, adding a new contact manually or right on the lead contact timeline.
How Route distribute the leads among Agents?
The distribution is a random process.
Every time a new lead enters Route all of your Agents will have the same chance of being assigned to this lead.
Next: How to invite New Agents?