Audiobooks on Ipad?

I want to use audiobooks on Ipad.
In what way can I do this?

I'm not sure what your question is, but I use the Audiobooks app. There are plenty of free books, as well as the ones you can pay for.

Are there other ways?
Sometimes I receive books as files (by mail)?

Overdrive will let you checkout from your library if they use it and also have audiobooks.

There is the Audible app and website that lets you buy and listen to audio books on the iPad.

And if I get a book as a podcast?

You can open iTunes on your pc or mac and import the file and then synch it to your iPad.

When you import a book into iTunes, right click on it and choose Get Info. Go to the Options tab and make sure Media Kind is set to audiobook. Otherwise it will treat it like a music file. You want it to know it is an audiobook, that way it will remember your place.

You set up syncing for audiobooks under the Books tab when the iPad is plugged in (or set for wi-fi syncing). You have to check the box to include audiobooks, then select all or selected books.