corp tax- TTP and tax adjusted profit

I’m getting quite confused when working out corp tax and have hit a wall and as home studying its a bit of a nightmare!

example below

So we have Profit before tax
add back
depreciation,
non trading loans,
donation to charity,
gifts (non allowable)
capital expenditure
etc
Then less
Bank interest
loan interest
Capital allowances
etc
Gives tax adjusted profit.

Then to get to TTP some of the things adjusted above are put back with some other adjustments.

I cant get my head around what I’m doing here, why are we taking things out then putting them straight back afterwards,

For tax adjusted profit non trading items are removed along with non allowable items like depreciation and certain gifts, But I don’t understand the movements to get from here to the TTP amount and want to understand it rather than just attempt to memorise which ones I’m moving

Thanks in advance and hopefully that makes sense