How do I email all current members?

First, create a new audience. Navigate to Emails > Email Audiences > New Audience.

Select Standard Email Audience and name it. This audience will dynamically update, so name it something that will make sense in the future as well. 

Under the Component List section of your audience detail page, click Add New Search. 

This will take you to the search criteria page for the Email Audience Report. In addition to the default criteria, add the following criteria to limit the scope of the search to include only active members.  You can further limit this audience to a specific membership term or terms using the "Membership" search field, but for this example, we will include all members.

Membership Expiration Date: Greater & Equal CurrentDay
Membership Status: Equal SUCCEED

Select Load Criteria and then Run Report.

If you are satisfied with the results, click "Save Email List" to save this search to use for this email audience.