I want to finance my company with my personal money (to buy some stuff).
What is the best way to do that in an accounting point of view?
Shareholders can lend money to companies, no problem. You should properly document it, of course. We use Quickbooks, and one of the accounts in there is "proprietor's loan" - we record in there when we lend the company money, and when it pays us back. You don't have to charge interest and life is probably simpler if you don't. The company repaying the loan is not a salary for you so you don't pay taxes on it personally when you are repaid.
This can also go in the other direction: the company can lend you money. However, before you think this is a great way to never pay taxes again but just borrow from the company for the rest of your days, there are restrictions on that, and at a minimum you have to take into income the interest you would have paid on such a loan from anyone else. (Here's an article from a company that wants to make money offering you financial advice, but it seems correct.)
Our company is over 30 years old and that account still exists. The main use for it these days is "I bought a personal thing with the company credit card [by mistake or because my personal card didn't work], so that means the company lent me the amount of the purchase" and the inverse.