Bad quality images after export

What resolution are the images. You must have 300 dpi for print.

I think when you say "export," you really mean "import." When you bring an image onto the page, some programs call that importing, but InDesign calles it "placing." If you are using a copy of InDesign with a non-English interface, it might be called something different, but it's in the File menu.

What you see on the page isn't necessarily what you get, though. When a high-resolution image is viewed on the screen, it takes some time for the computer to render the digital info into pixels, and if you zoom or move around on the screen, it has to redraw those pixels again. This can take time, so InDesign defaults to showing you a lower-resolution image that is good enough for most placement issues. When you output the page to a printer or PDF, the low-resolution preview image is replaced by the actual image info, which is usually better. If you want to see the full-resolution image, you can go to View>Display Performance and choose High Quality Display, but your system will be a little slower. You can also show all of the images as grey blobs if you choose Fast Display, which you might need if you had many high-resolution images on a page, and you just need to edit the type.

The actual resolution of the image is a combination of the image's resolution (if it's a pixel-based format), plus the scaling. If a 300ppi photo is scaled up to 200%, it's resolution will be half, or 150ppi. Reduce it to 50% and it will be 600ppi. You can see the actual and effective ppi in the Links window. Vector images don't have a ppi, so you can scale them without changing the resolution.

images taken from Internet sources are generally too low-res for print. In addition, most of them will be covered by a copyright that would disallow you using them for your own publication.