When quoting a piece of text, you traditionally use square brackets to mark any part of the quote you have changed from the original for any reason.

For example, suppose that I say the following sentence to you in an interview:

"He gave me some cheese"

You decide to quote that sentence in your article, but you realize that it may not be clear to the reader of your article who the "he" refers to if all they see is that sentence. You know who I meant, because you heard the whole conversation, but the reader didn't. You need to change my quote to make it clearer. But you also need to clearly mark where you changed the quote, because it is important that you don't put words in my mouth. So you write:

Over a glass of domestic claret, Biglig admitted that "Calacanis gave me some cheese"

sic is the opposite. You use it when the quote contains a mistake, to explain that the mistake is in the original, and you know about it, but are copying it because you want to quote the original accurately.

For example, you read in my new book a sentence "That bum Calcalancis never gave me any cheese". You want to quote it, but you see that I spelt Jason's name wrong. If you leave the misspelling as is, maybe people will think you spelt it wrong! so, in you article you say:

As Biglig wrote in his recent polemic pamphlet, "That bum Calcalancissic never gave me any cheese"

Then everyone knows it was my mistake.

Now, in your specific example of a quote beginning "Government said" then, as drivorobot says, the change is simply that in the original source, the g was lower case (because it was half way thru a sentence) but in the quote, it began the sentence, so had to be changed (because of the laws of grammar) to start with a capital, and since it was changed, it has to be marked with square brackets.

By the way, when you see this, it's worth asking "I wonder what was in the first part of the sentence, before the word government?" That's why the square brackets are there, to make sure you can see what has been edited.

The brackets "and "" are used to show when a letter has been changed from its original form in a quote.

The bracket apparently changed to code here on the site, so I can't see what you're saying exactly, but usually the brackets is the way a print journalist will show that the first part of the quote was left on. The bracket indicates something came immediately before the quote or that the quote is not complete. sic is how it is displayed sometimes too.

Because in the original text, that word was the first letter of its sentence and had to be capitalized, but when it is quoted they change the capitalization to fit its place in the new sentence.