You have learnt to create a Google+ Page already. I hope it would help your brand, business or organization to engage with interested Google+ users and customers to convey your up-to-date information of your business, brand or organization. It will also enables you to find interested people in your niche and it is an opportunity to reach more users too. But after creating a Google+ page, did you try posting or commenting on your Google+ page as itself? Or did you ever wanted to comment on another Google+ profile as your page?
Google+ introduced business page feature to represent your brand, business or organization. So you can use your Google+ business page to inform whatever goes officially or unofficially with your business or organization to your followers and customers. Also sometimes you may wanna comment as your page to respond to your followers or to engage with an discussion too. However if you directly visit to Google+, it will use your personal Google+ profile by default. But to post or comment on your page or elsewhere as itself, first you need to switch to your business page. If you couldn't figure out how to post or comment as your page, now you can find out how to.
1. Sign in and navigate to Google+.
2. On left sidebar, hover your mouse over Pages icon.
3. Now you will see pages you administering on Google+ and click on preferred page name to switch to your page. Now on you will be able to post and comment as your page until you switch back to your personal profile.
Note: If you wanna switch back to your profile again, hover over pages icon on sidebar and click on your profile icon with profile image.