Manual input of income and expenses

Hi, I have a very simple business model and I'm not very good with IT, but I do understand book keeping. I want to enter income and expenditure manually, but the entries, incomes and expenses are doubled up, making a nonsense of the whole thing? Also I can't delete one of each of the doubled entries. Please can you tell me how to stop the system 'doubling' everything up? And if I make an error. how to delete an entry? With best regards