Assign New Lead Records to a Salesforce Queue

To assign Lead record to a queue Manually:
You cannot specify a Lead owner while creating it, however, once the lead record is created, you can change its owner and assign it to the queue. Follow below steps to do so:

1. Open the newly created lead.
2. Go to Details tab
3. Click on the 'Change Owner' icon on the Lead Owner field
4. Click on the dropdown arrow for People icon on appeared window & choose Queue.
5. Check mark 'Send Notification Email' (Optional)
6. Click Change Owner

To create new Lead record in bulk and assign them to a queue:
To achieve the expected functionality, you need to create a process using Process Builder and assign it to the Lead Queue.
Steps involved before importing lead records are as follows:

1. Go to Setup >> Process Automation >> Process Builder & create a new process.
2. Specify a Process Name
3. Choose "A record Changes" option under "The process starts when" field.
4. Click "Add Object"  and choose "Lead" under Object field
5. Choose "Only when a record is created" under "only when a record is created' field.
6. Click Save
7. Click "Add Criteria"  and define "Criteria Name"
8. Choose "No criteria—just execute the actions!' under "Criteria for Executing Actions"
9. Click "Add Action"  and choose "Update Records" under Action Type" field
10. Define the "Action Name"
11. Click "Record Type" field and choose "Select the Lead record that started your process"
12. Under "Set new field values for the records you update" specify the following :
Field : Owner ID
Type : ID
Value : <Lead Queue Id> (eg. 00Gxxxxxxxxxxxx)
13. Save the changes
14. Activate the process.