I use the Add Meta-Tags plugin, click the name to get to their site to download the latest version. I do sometimes go into the Editor and add the meta-tags right in the code, but that is for more experience or risk-taking people. I do consulting if you need any help.
After you install and activate the Add Meta-Tags plugin it will be listed under the Settings menu, select it and when it opens fill in the spaces being sure to read what each one is about. Note: each theme handles the home page title differently, so be sure to pay attention to that. Now, copy the code above and insert/paste into the third box down titled, “Provide the full XHTML code of META tags you would like to be included in all of your blog pages.”