Addressing the question in point:
A Locator Approach is one where the primary aid is a compass locator, which as you correctly point out has a significantly lower power output. The Locator will always be situated on the extended centreline of the landing runway, at approximately four miles.
Similarly, an NDB Approach is flown using the primary aid of an NDB, although the NDB may be positioned either on the airfield, or at either end of the landing runway extended centreline..
Regarding your second query, an NDB/DME approach is an approach that is designed to be flown using both the NDB and the DME. If the DME is not available you may not fly the approach, but may instead be able to fly an alternative NDB approach - which will be of a different profile, and will usually be subject to increased minima.
I hope I have not misled you, but stand to be corrected.