The points of reference are circled in red in the below image. Look at how the open string (Fret 0) and Fret 12 feature the same notes, but an octave above. The note of A appears three times so we can already see there’s a relationship between Fret 5 on the 6th string, and Fret 12 on the 5th string as well. We’ll explore this further as well.
This is just a guideline and there are literally thousands of options out there for each piece of equipment. Do your due diligence and research each piece before you purchase. As with most things, you get what you pay for so if you have the budget, I would splash out on better equipment where possible.