This is a great question. CBD and THC are both the two most well known cannabinoids within the cannabis plant. They are at varying % within different strains. So for instance, you may have a strain that has 1% CBD and 19% THC. This is important because it has an effect on how you will ultimately feel.
CBD is non psychoactive and is both an analgesic as well as an anti inflammatory. Many people report that they feel very relaxed and can even become a bit sleepy taking a lot of CBD. CBD also works in synergy with THC which is called the entourage effect.
THC is the psychoactive, mind altering cannabinoid, which is why it is so well known. It also has medicinal properties and can help take pain away, induce an appetite among other things.
A new edible consumer should be aware of what they are looking to treat. If for instance you are not looking to get high, you may want to find an edible that is primarily CBD either at a 1:1 ratio or a very high ratio or with no THC at all.
Most edibles are very high in THC. A bar of chocolate may contain 180mg of THC in total and the suggested dosage may be 10mg. Everyone reacts differently, for me, I get very uncomfortable going past 5mg. A standard dose may be 10mg for some people and 20 for others. To give you a benchmark, 2.5 mg may effect you like a glass of wine, at 5mg most will feel some psychoactivity and at 10mg most people will feel stoned or near stoned. Everyone is different!
When starting with edibles, always take a very small dose and wait 2 hours. Here is an article I wrote on this topic. I hope this helps!