Open an account at a trusted online casino
Go through the account verification procedure, if needed
Choose the most convenient, low-cost payment method, available in your country
It would be great if you can use the same payment method for withdrawals
Decide on the amount you would like to deposit (the min deposit in most casinos is €10)
The money should appear in your online casino account in a few minutes (unless you choose Western Union, Bank Transfer, Boleto, etc.)