Before getting your tuner out to tune your 12 string acoustic guitar, please keep in mind that there should be 6 pairs of thick and thin strings on a 12 string guitar, you might also get confused what tuning key to turn as well but you will get used to it soon enough. Also note that when i say Low E it means just E nothing more.There are many other guitar tunings but what you about to learn is a standard tuning for 12 string acoustic guitar, no tune down or anything.
Now, to tune a 12 string acoustic guitar, go get your tuner (every musician should have one) and just tune the main 6 strings to ordinary tuning: E A D G B E low to high, start tuning the 1st string from (the highest sound string) to E.
Next, skip the thiner string and you find the 2nd string, tune that to B and skip another thin string and tune it to G > A and Low E. Just keep skipping those thin strings and you should finished your main 6 strings in no time.
Here comes the tricky part, to tune 12 string guitar on the rest of the strings, let's start from the high E the tuning key should be on the right hand side if you hold guitar head up with fretboard facing you.
Just tune those first 2 thin strings to high E and high B. Don't worry if they still a little out of tune, go through other strings so they are stretch equally. Next, go to the 2 tuning keys on the top right, on the top tune this to G one octave higher than normal. And the rest strings are as you can see in the picture.