How can I write a novel? Should I introduce the hero in detail and then the heroine, or should I simply carry both of them?

Don’t write it in English, write it in your native language. I have no idea what “carry” means in this context and I’m pretty sure it isn’t some specialist “novelist-speak”.

If you have a plot in mind then - as I see it - you need to figure out how it will unfold over the course of the story. Detailed descriptions of the characters will be tedious and they get in the way of the story. Let the character details emerge in the course of the story. Don’t just tell the reader that Liam is greedy and overbearing. Give the reader cause to believe - via the action - that Liam is greedy and overbearing. Perhaps he has just ordered the biggest dinner on the menu and is now haranguing the waitress because she got some tiny detail of his (picky and pointless) order wrong. Perhaps she’s crying because he’s so horrible.

Show that your hero is the hero. Don’t tell us that in advance. Make him heroic by his actions.

Still don’t know what you mean by “carry”.