Understanding Correspondences is one of the very basic steps in becoming a successful witch... 
In most Traditions, whether it's a Wiccan Tradition, or a Witchcraft Path, we practice what is called 'sympathetic' magick. So, when we say correspondence, we are talking about the connection between non-magickal items and magickal concepts.  

A Correspondence table or chart is like a cheat-sheet... It allows us to choose the correct ingredients for spells at a glance. There are correspondence tables available for all sorts of things. They list how the energetic and metaphysical connections between spell components respond to each other. 

A correspondence table, however, is just a tool. It is a way to make writing your own spells or rituals easier, but it should never be considered a hard & fast rule. Throughout different Traditions or Paths you will find that different practitioners may assign different meanings to things, and their correspondence tables may not match what you are used to seeing. Each Witch finds different meaning in different symbols. Many Witches create their own correspondence tables, due to their own experiences & belief system. The fact that it may be different than usual does not make it Wrong... only different. 
When you choose a correspondence table, you should carefully read through it... If it fits into your personal belief system, if the correspondences for the symbols involved match what you believe, then you can add it to your BoS... If they do not match, either find a new table, or create your own. Just Remember, there are no right or wrong correspondences, only differing ones.

With Herbal correspondences most beliefs follow the norm. By this I mean that you will not find many differences between one correspondence table and another. This is because the herb has certain healing abilities, and the correspondences are usually based on that. You might find that the Planetary correspondence for a certain herb is different, for example; Some correspondence tables will list Jupiter as the Planetary correspondence for Cloves... which to me is a Fire element and therefor the planetary ruler is the Sun... and there are correspondence tables that list the planetary ruler as the Sun... so, I would either list both planetary rulers... or simply exclude Jupiter, as it doesn't fit with my beliefs about Cloves... This is called 'Choice' and it is Always your right to Choose... it's up to the individual to choose what is right for them, it's neither right nor wrong, simply different.

How do we choose? 
The best way is through experience. After you have practiced witchcraft for awhile you will have a better understanding & feel for what is going to work for you. Until then the best thing to do is to find a site that gives knowledgeable advice and try it out for yourself. I always tell people to Research... Read everything... Knowledge is true power, and the more knowledge you have, the better magick will work for you.

Knowing what, when and how to work a spell will ensure that the chances of the spell working are greatly increased. 
What spell ingredients to use.
When is the best time to work the spell; taking into account the day of the week, the Moon cycle, the hour of the day or night.
How to perform the spell; how to mix or use the ingredients... how to call up the energies needed... How to incorporate it all into a working spell.

Correspondence tables will aid you in doing all of this. 

~Love & Light~
     ~Mary~