Memtest cycles through I think 9 or 10 different tests that basically stress the memory in a number of ways by applying different patterns to every physical address area on your RAM...test 7 is really what you're after for stability which is random number sequences
Reading it should be fairly straightforward, the top area displays basic information and what the test is doing, and the bottom half will list any errors that may come up and where they occur. Overall, you want memtest to pass, if it doesn't pass, you have errors. Obviously if the bottom half of your screen gets filled with red indications of when and where the error occured
Do note that memest stable does not equate to windows stable, memtest can cycle for hours and be fine but crashes immediately in windows. Memtest should just be prilimary testing to rule out ram issues, then you should test in prime95 or something similar
Even then it would probably be better to manually set most if not all memory settings, for example defaults for me would result in BSODs since 2.5cas + 2.6vddr = BSOD. Specifically max async latency and vddr don't go together nicely