Engine oil at Yaris I……?!

Hi together! Especially to those who, like me, have the Ier Yaris. Which engine oil do you drive, already changed (viscosity, not the oil, is clear or ) and what experiences did you have with it? I will change next week. Have since I bought it (Nov 06) 10 W 40 in it and will change to 5 W 30. Meaningful or rather not? The whole then Castrol Magnatec 5 W 30. Have always had good experiences with Castrol at the mopped. Could someone ever lay of course e explain what the numbers (10 W 40, 5 W 30, 0 W 60 etc) mean? I know where you can switch to where, but I don’t know what the numbers mean. Thx Greetze