Click on the User who's login history you want to view.
On the User's page, scroll down to the section called 'Login History' at the very bottom. You can view recent logins, and download a .CSV file of up to the last 6 months of login history per User.
View Org-Wide Login History
Navigate to Setup > Administration Setup > Manage Users > Login History.
You can download a GZIP or .CSV file of the last 6 months of login history for your organization.
View Your Login History
Navigate to Setup > Personal Setup > My Personal Information > Personal Information.
Scroll down to the bottom section called 'Login History'. You can view recent logins, or download a .CSV file of up to the last 6 months of login history.