Sole Trader and PAYE

Hello there, I'm currently working a company as a employee earning around £40,000. I want to set up Amazon FBA account to sell goods on amazon store, after researching i think i will set up as Sole Trader. I know that i need to complete my Self Assessment each year but im not sure on few things: So e.g. if i earn profit of £13,000 on selling Amazon and when to complete Self Assessment: do i need to pay just tax on the £430 (because after minu tax free allowance £12,570) OR do i need to include 40,000 whcih I'm earning as an employee and pay 40% tax because if i add 40,000 + 13,000 = 53,000 ? Could some clarify this for me please?

Hi,

A resident of the UK is taxable on their world-wide income. A Self Assessment Tax Return is used to declare your world-wide income and tax deducted, in one calculation.  
The tax return has different sections for different types of income and capital gains. A paper tax return is made up of SA100 and several supplementary pages.  

Self Assessment tax return forms

There are several type of income that prevent the use of the online tax return. In those situation, it is possible to purchase a commercial tax return, provided you have a Government Gateway user ID and password. Have a look at below for more information.

Self Assessment tax returns

Thank you.