Adding depreciation entry

I am trying to show depreciation of assets on my accounts, and from looking around I belive that I should add a journal entry, but I have tried to credit 0020 and debit 0021, which just moves the figure into the 0021 box, but this has no effect on my P&L which I am trying to reduce. Can anyone help a novice please.

It’s the other way around:
Dr 0020
Cr 0021

Generally, accounting is opposite to what it should be. But in effect, your debiting the plant machinery account (therefore lowering your costs effectively), and crediting the depreciation account.

Hope this helps

You need to debit 8001and credit 0021

Thanks for the help, I think it is working now