It is, essentially, educated guesswork.
You use the peaks to identify environments, adjacent hydrogens, the number of unique environments etc. and using this information you can build a structure.
After you've got a structure (I suggest drawing it out in skeletal form) you can compare it to the NMR to double check its correct.
Perhaps start of with a few NMRs of simple alcohols and esters to build up your ability.
Thank you so much. That was helpful!