When foreign chemicals are present in your blood stream, your body needs to expell them. Depending on their chemical make-up some of them can just be removed right away (like d-amp some of which comes out in your urine the exact same as it went in) however others first need to be metabolized (broken down or otherwise changed) to be removed.
Different chemicals are metabolized in different ways and even the same compound might have different metabolic paths (changes it undergoes) to leave your system. These chemical changes are caused by enzymes. In order to extend the effect of a certain chemical, you want to prevent the chemical (or its active metabolite if a pro-drug) from being metabolized. A very common first step of metabolization is oxidation via a group of enzymes known as the CYP [Cytochrome P450] family. That chart lists different enyzmes in the family (e.g. cyp2d6, cyp3a4), what substances they metabolize (substrates), what substances cause them to metabolize better (inducers), and what substance cause them to metabolize worse (inhibitors).
To properly use the chart you have to understand the metabolic pathway of the substrate and what the enzymes are actually metabolizing it into. For example CYP2D6 converts hydrocodone into hydromorphone which is more powerful and generally desirable so you would want to induce it (while inhibiting CYP3A4 that converts hydrocodone to norhydrocodone). However oxycodone is already much stronger in its ownright and CYP2D6 will remove it so you would want to inhibit it to get a better high. Other substances like morphine don't undergo primary metabolizism via CYP (instead starting with a phase II metabolic reaction like glucuronidation).
