If you would to understand the fundamental concept and basics for HMBC, you should browse the following links with supportive examples. I assume that you have to differentiate between two structures on orientation, for instance, or to have interpretation to your spectra analysis.
AS par Priyani Paranagama madam mentioned HMBC always give long rang coupling of C and H( 1H-3C relation) means if in your HMBC spectra dots are very prominent or dark then make line H-protion axis exact matching C- carbon axis if they matching accurately it means your 1Hproton connected with 3C position your carbon(1H-2C-3C).(1H-2C you can get by HSQC)
The interaction between 1H and 13C, in terms of NMR coupling terminology and/or topology, is defined by nJCH where n can be 1, 2 and/or 3. While 1JCH is known to reveal direct correlation, 2JCH and 3JCH are known to reveal long range correlation. They are also known as one-bond and multiple-bond correlations respectively. While HSQC experiment reveals 1JCH, HMBC experiment reveals 2JCH and/or 3JCH. While the magnitude of 1JCH is in the range of ~120 Hz to ~170 Hz, 2JCH and 3JCH are in the range of ~4 to ~14 Hz.If one expects to have the range of 2JCH and 3JCH then, the HMBC experiment has to be performed for different values, say 6 Hz, 8 Hz, 10 Hz and 12Hz.
The interpretation can well be accomplished if one records both HSQC and HMBC experiments and compare the results.
Last but not least, one point has to be remembered. A typical JHH value can match 2JCH and 3JCH values. So, one has to be careful while interpreting a HMBC result.
My recommendation is to record HSQC and HMBC on a small molecule such as ethylbenzene (which is usually supplied as a reference standard along with an NMR spectrometer system by the respective vendor) and start analyzing the results.