What is the main and major difference between Current tax system and flat rate tax system? And what is value added tax system? I did some research and read few articles, but they are all hard to grasp. Please help me in plain english...

Current tax system uses aggregate rate on income, that's why we have different tax brackets. The more money you make, you pay a higher RATE, (not just a higher amount with the same rate).

Flat rate tax system charge everyone the same percentage, regardless how much the tax basis is.

Value-added use a certain rate for tax calculation, but allow you to deduct the tax you paid (say material), so as a result, you are only paying tax for the part where value is "added". For example, you buy metal wires at $2 each, you twist them into funny shapes and sells them for $3 each, Value-added system just tax on the value added portion, $3-$2=$1.

Of course there are a lot more rules on each to make them as confusing as they are, but these are the basics.