Any user can be assigned to a lead. Assigning user to a lead will result in the todos of that particular lead to reflect in the users My Todo List. In addition the user will start receiving notifications for that particular lead if his Notifications setting is set to Follow my leads.
A user can be assigned to a lead directly from Pipeline by dragging the user profile pic located at the bottom right on to the lead.
The lead can also be assigned to a user from the lead details page. To assign a user to a lead click on the lead in the pipeline.
Start typing the name of the user whom you want to assign the lead to- a dropdown will appear suggesting names. Select a name from the dropdown list to assign the lead.