Commas can be tricky. They have several uses. Below are some of the most common. You should use commas to separate clauses (sections) of complex sentences. For example:
After talks broke down, relations between the two countries became even more strained.
Words like 'however,' 'consequently,' 'instead' and 'therefore' should have a comma after them if they are the first word in a sentence. For example:
However, there is evidence to contradict this approach.
Before the words 'and', 'but' and 'because,' you can either use a comma or leave it out, but if the sentence is long and complex, a comma can make it easier to read (as in this sentence). To take another example:
The talks were conducted against a background of increasing distrust between representatives from both side, and relations between the two countries consequently deteriorated.
Commas separate items in a list. For example:
Relations between the two countries were characterised by distrust, hostility and caution.