Dolphin 7.1 is somewhat limited in the Meta Description and Meta Keyword department, but there is one area in the Administration that you can add these to.
The drawback is that they are only for the Homepage.
To add or update Meta Description and Meta Keywords simply login to your Dolphin 7.1 Administration Dashboard. Then, find and navigate to:
Expand the General section in the middle part of the page near the top. Now fill in the "Homepage meta-description:" and "Homepage meta-keywords:" box/areas scroll down and save the changes.
You might also consider clearing the Dolphin Template Cache after doing so just to make sure the entries are updated.
To do so go to:
Under the Clear Cache area click the "Templates" link and that's it.
Visit and refresh your Homepage. View the page source with your favorite web browser and make sure that you see the Meta Description and Meta Keywords that you just added near the top of the page between the <head> and </head> tags.
If you are looking for additional control and more on site SEO optimization for other pages and areas of Dolphin 7.1 you can check the Boonex Market for SEO Modules. There were a few for Dolphin 7.0.x, which might be updated for Dolphin 7.1. If they haven't yet, then I would expect to see more of them in the near future.
You could possibly do some manual tweaking and changing page code and in the database for other pages if you know what you are doing, but it can be a lot of work.