Lookup anther sheet as reference

[Por2gal]

hello supportive members,
I am a novice at using formula's and would like some help with the lookup feature set from another tab.
I have attached my expectations, but cannot understand how to use the lookup feature to add to the final sheet.
Or should I be using another formula.
I want to add data to one sheet and have it automatically added to the relevant months.
Or should I add data to the relevant months and have it automatically updated to 'finalsheet'?

Please Help
thank you
Diana
p.s I have tried to use a 'cashbook' template to set this out, but I keep loosing the lookup feature

[TMS]

Got to be honest and say you would be far better off if you had all the data in a Structured Table on a single worksheet. You can then easily sort and filter the data, and use Pivot Tables to analyse it.

Excel works much better if you record your data in a simple two dimensional matrix format.

If you are constantly trying to enter data into multiple sheets, you are opening yourself up to a world of pain.