enter your wages

Salary from a permanent job as an employee does not belong in the business accounts of your own company/sole proprietorship

How does this work with personal income tax? This must also be registered, right?

All this information can be found on your pay slip. To help you complete your tax return correctly, your employer will provide you with your tax form 281.10 each year. This form contains the yearly information about your salary with the corresponding codes, which you must fill in in box IV of your tax return (part 1 of the return).