Kamen Rider Cards?
 

I love these cards!

...what do i do with them?

If you have a DecaDriver, you can sorta use them with it.

explain more?

I'm not sure if I can explain it very well. :(

Seeing as all of those are of Riders that came after Decade, inserting them into the DecaDriver will probably result in it saying "Attack Ride (Final Ride for the Kamen Rider Aqua Card, since it's a yellow/golden card)" and then when you close the belt, it'll make the standard activation sound. It won't say the name of the Rider.

You can also use them in a Ganbaride Card Game Machine in Japan

They work (or at least did - I'm not sure if they still have the card readers) with an arcade game called Ganbaride. You'd put cards (or Gaia Memories, or Core Medals, or Astro Switches) into the machine to unlock special attacks or abilities. I think the prize for doing well is just more of whatever the gimmick is (the machines have gotten updated for each Rider series - the cards are from when Decade was the main show). I thought the machines worked solely off of Astro Switches now, but those cards are from more recent shows and movies, so I guess they still take cards, too.

You can also put them in the DecaDriver and get some special sound effects.

hmmm...but we don't have any Ganbaride's round these parts and the DecaDriver will only make the standard sounds for all those cards eh?
I got a bunch more now that came with some toys, ah well...that kind of sucks.