I can’t speak for the specifics of how to use bidets, but in my experience the general idea is to use them to supplement your daily hygiene rather than as a replacement for toilet paper.
Where I come from (the Mediterranean), it’s not customary to take a shower or a bath every single day. Personally, it’s not possible because the frequent exposure to hot water dries out my skin and worsens my eczema. So the bidet is useful for keeping my private parts clean every day in absence of a full-body wash.
It’s basically a mini bathtub for your crotch. You don’t get into the shower every time you take a shit. Or do you?