Is it possible to leave a job when I want?
Normally in the first few months of any job it is possible to leave (or be asked to leave) at any time without any consequences for either you or the employer.

Normally a minimum notice period (advance warning that you want to leave) is required, but there are not necessarily any penalties if you are not able to give this notice.

Some jobs agreements may specifically state that a certain notice period is required and that the employer can deduct pay as compensation if the employer does not respect this. This type of agreement is relatively rare.

Will the employer have to pay me for all the time worked if I leave early?
The employer is legally obliged to pay you for all the time worked. Obviously if you suddenly leave the employer may not able to pay you immediately. However, he is still under an obligation to pay you in full.