All combinations of filters within a specific Segment are going to be "AND" filters. For example, you are looking for accounts that have had logins within the last 30 days AND have sent 0 emails within the past week.
But what if you wanted a segment that pulled accounts that have had no logins OR have sent 0 emails week?
To do this, create and save two separate account segments. One that meets your first set of criteria, and one that meets the other.
Once this is done, you can create a new segment and filter on Account Other Info> Segments. Use the operator "in any of" and then select your two segments.