What are the tax changes I need to know about when filing my individual return for 2012?

I am doing freelancing for two different companies and I have several questions. I deliver for them digital files, such as research, PowerPoints or excel files. Do I need to add sales tax to the invoices? When and how do I file taxes? I have never worked before in California and just started working in October last year.

Hello,

I am a Tunisian national on J1 Visa in the US. However, I have never paid taxes in Tunisia. I did my PhD and was working in France for 5 years paying taxes there. I got my visa in France. Is my tax residency France or is it Tunisia? Because if I claim it to be Tunisia, there is no two years tax treaty. If it's France, what documents I need to claim the tax refund?
Thanks

When can I file my 2017 tax returns?

What exactly is accounts receivable financing and factoring and how can it help a business?

What is the best way to become a financial advisor?

Which washer/dryer will qualify for an energy-efficient tax credit?

How many people actually go in for a Health Insurance? It is observed that most people think it is a waste of money so avoid it. What do you think?