You can cast a spell to help you gain money, but it won't simply land on your doorstep for nothing.
For example, you would need to try to improve your chances of earning money, rather than getting it on a silver platter; why not try casting a spell to help you get a promotion at work, or to help get a job if you don't yet have one, maybe for a little extra help on getting a bonus at work.
But alongside any spell you need to be working the mundane ways of helping yourself and always be careful what you wish for.
Dependant on how much you already know about the practice, you should either improve your knowledge of basic practices or learn how to write your own spells.
you might wish to narrow it down a bit. say you have a sudden bill, there are spells to help you get a specific amount for an emergency. you could also try job spells, spells to help you save, pay off debt quickly, or money charms to attract wealth. granted, like H2O mentioned, it won't rain money on you, you need to work for it and it will come like a bonus, or perhaps if you have a check in the mail for some work you did. you should get creative, but you have to combine practical work with magickal.