Any money the government takes from you (legally) for doing any economic activity is tax. Generally, this is a percentage of the money you receive or give. Taxes are either direct, where the money goes directly from your pocket to the government's pocket, or indirect, where the money goes from your pocket to someone else's pocket and then to the government's pocket
This is not exactly a word, but rather a verb that denotes the act of charging a tax. If the government charges or puts a tax on something or someone, the act of putting that charge or collecting the amount is known as levying
This is a tax on tax, levied by the government for a specific purpose. Generally, cess is expected to be levied till the time the government gets enough money for that purpose.