One can access and login Google+ (if he has already joined) directly from his Gmail account. A tab with "share" button is been shown at the very right of your browser.
To directly login to Google+ you just need to type https://plus.google.com/ in your browser and log in with your user name and password.

If you want to log in from your mobile just type https://plus.google.com/ in your mobile browser and log in.
One can share videos, share thoughts, images or just say a HI to all his friends with Google+.
[via - searcharge]