This is just about the most basic concept in language. Note that every known language in the world has the ability to construct independent and dependent clauses. Knowing this fact makes your life easier when you come to learn a new language. Knowing how you do this in your mother tongue makes it easier still!! Because then all you have to do is say to yourself: “Ok, this is how I do it in my language, how do they do it in the target language?” Answer this question and you are well on your way to an in depth understanding of how the target language works and you are immediately leaps and bounds ahead of 99% of all other people engaged in learning that language.
So yeah, it’s kinda important!!
So how does it work in English? Well, it’s actually pretty simple and pretty formulaic. Which means it can be memorized. And then you will write like a pro! 🙂 Almost everything you need to know is very neatly and nicely explained here:
However, please note that although number two above shows you how to correctly use a semi-colon, in reality this is very infrequently used nowadays. Most people will either use a comma, eg.”Tom reads novels, however, Jack reads comics” or split it into two sentences, eg. “Tom reads novels. However, Jack reads comics.” As most of YOUR sentences will be expressing more complicated ideas than that, may I once again strongly recommend splitting them,eg. “X. However, Y” as X, however, Y is damn ugly (too many commas).
Please also note that the subordinating conjunction ‘so that’ can also be expressed with the one word ‘so’, which is admittedly confusing because ‘so’ is normally a coordinating conjunction and would therefore be preceded by a comma. Here’s how it works, using a sentence that came up in the CAE Result student’s book:
1a. The shops were closed so (that) I couldn’t buy anything.
Here ‘so’ means ‘so that’ and it introduces a dependent clause (also known as a subordinating clause) i.e. I couldn’t buy anything. The whole sentence could be rewritten as:
1b. The shops were closed in order to prevent me from buying anything.
Which would be unusual but is possible. You can clearly see that there is a relation of dependence between the two clauses/ideas being expressed in the sentence.
In the following example:
2. The shops were closed, so I couldn’t buy anything.
We have two independent clauses (also known as main clauses) joined together. Here ‘so’ is a coordinating conjunction which simply links two ideas, or complete thoughts, and a comma is required.
The same idea in 2 could also be expressed (and more clearly defined) as:
3. I couldn’t buy anything because the shops were closed
‘because’ is a subordinating conjunction and once again no comma is required.
Hope that helps, but if you find it all to dry and theoretical then just do what natives do: don’t worry about it!! 🙂