MemTest86 and Memtest86+ are memory test software programs designed to test and stress test an x86 architecture computer’s random access memory (RAM) for errors, by writing test patterns to most memory addresses, reading back the data, and comparing for errors. Each tries to verify that the RAM will accept and correctly retain arbitrary patterns of data written to it, that there are no errors where different bits of memory interact, and that there are no conflicts between memory addresses.
In other words - in plains English, memtest86+ will run through your RAM and tells you if they are OK, or not.
To be safe rather than sorry, it is good practice to test your RAM to ensure they are working as designed. Always run this test when you first build (or purchase) your computer. And re-run this test once every year or two to verify that your computer is still working as expected.
Now that you have a background of what bad RAM is and memtest86+ is. We’d go to the important bits next - how to run memtest86+.