What does this bidet seat come with? Do I need anything else for install?

This bidet seat comes with everything needed to install and operate the bidet seat on a normal toilet. If you have a skirted toilet and thus don’t have access to the bottom side of the bolts that connect the toilet seat to the bowl, you may need additional hardware, which you can find below:
Alt T connector: https://www.manybidets.com/product/bidet-t-valve-for-skirted-toilet/
Top Mounting kit: https://www.manybidets.com/product/swash-bidet-seat-top-mount-mounting-hardware/

If you have hard water, you may also consider pairing your seat with a carbon water filter, which can be found here: https://www.manybidets.com/product/water-filters/

If using the filters, you’ll want to make sure to change them out every 6 to 9 months.